Re: [Tutor] General method for creating a partitioned window
Am 09.08.2011 16:44, schrieb Shwinn Ricci: I am using wxPython and OpenGL, although I would prefer to run a script in Maya, but this does not seem efficient for what I want to do, since maya only allows for 3-D visualization, not simultaneous 2-D/3-D viewing (i.e., side-by-side) On Thu, Aug 4, 2011 at 7:37 PM, Alan Gauld alan.ga...@btinternet.com mailto:alan.ga...@btinternet.com wrote: On 04/08/11 20:52, Shwinn Ricci wrote: Say I want one half of a 720 x 480 window be dedicated for creating a 2-D structure, and the other half for a 3-D structure. There would be a line 1 or 2 pixels thick straight down the window that would divide the two sectors. How does one go about doing this without creating two separate GUI window frames? You would need one frame (or widget) with an opengl context with 2 independent viewports. I don't think that's supported by any framework. You probably have to use two widgets. But that's no problem, as long as you can use layouts and styles to get the desired appearance of the two widgets (i.e. to make them appear as one). I do not have my code with me right now, I can post as soon as I have access to it. You need to give yus more detail. This kind of thing is very GUI frame-work specific. Are you using Tkinter? wxPython?, Cocoa on MacOSX? They are all different. And because you want to do graphics you also need to tell us what graphics toolkit you are using? OpenGL? Something else? Or are you trying to script Blender or Maya or some other 2D/3D modelling tool? -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ _ Tutor maillist - Tutor@python.org mailto:Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/__mailman/listinfo/tutor http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] How to get the keys of a dict inside a dict. ValueError: too many values to unpack
Am 07.08.2011 17:37, schrieb Kayode Odeyemi:
Hello all,
Please I need help figuring out this permutation.
I have a dict like this:
x = {'pk': 1L, 'model': 'trans', 'fields': {'updated': 2011, 'tel':
3456}, {'pk': 2L, 'model': 'trans2', 'fields': {'updated': 2011,
'tel': 34510};
This is not a dict, it's a tuple of two strings. (By the way, the ; is
only needed if you would want to place several statements in one line,
which you shouldn't do.)
A tuple of dicts would be:
x = {'pk': 1L, 'model': 'trans', 'fields': {'updated': 2011, 'tel':
3456}}, {'pk': 2L, 'model': 'trans2', 'fields': {'updated': 2011, 'tel':
34510}}
Note the additional closing } for each entry. You can loop over the
entries of your tuple and check the type:
for entry in x:
print type(entry)
Now you can extend this loop and loop over the keys and values for each
entry:
for entry in x:
for key, value in entry.items():
print key
print value
If key is fields then value is another dictionary. So if you wish you
could also get the entries of those dicts explicitly:
for entry in x:
for key, value in entry.items():
print key
if key == fields:
for field_key, field_value in value.items():
print %s % field_key
print %s % field_value
else:
print %s % value
For string formatting used here see:
http://docs.python.org/library/stdtypes.html#string-formatting-operations
HTH,
Jan
#loop through and get the keys of each
for k,v in x:
keys = dict(x).keys()
print keys
I get ValueError: too many values to unpack
Any help will be much appreciated.
Regards
--
Odeyemi 'Kayode O.
http://www.sinati.com. t: @charyorde
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Re: [Tutor] Object Management
Am 27.07.2011 15:51, schrieb Alexander: Hello everyone. I'm having trouble wrapping my mind around a project I'm working on. My goal is to create a program that manages (allows its users to manipulate, search by criteria and edit) objects. There is one type of object, for example I'll say it's a car. There will be a central data file containing all of the cars and multiple users will have access to it at once. I'm having trouble here, I've done some research on MOO and twisted but I'm not sure where to turn. Sounds familiar ;-) ... on the way a lot of question are likely to arise. Like, OK, I've got a database. Do I load all the data at once to the client or only on request? What about concurrent usage by different clients (users)? How about authentification and authorisition? If I build a rich client (a python programm with GUI and network connection to the database), how do I manage the objects on the client? As James already hinted, there're fantastic python web frameworks. They have solutions for almost all the questions that will cross your path. There're some relgious wars about which is the best. In my opinion Django is the best for starters. Do some tutorials, read the Django book and you'll get an idea about the overall architcture, models, views, templates, etc. Additionally I'll need a GUI! tkinter? Does anyone have any suggestions on how to get started with tkinter? I'm overwhelmed with the amount of documentation I've had to read and think I have to read to accomplish my goal. I've written a rich client with PyQt which talks via web services to a web server. It's a lot of work! You have a lot of options, performance is amazing, but due to the complexity I would recommend to start with a web interface. If you really need or want a rich client, you should look into Dabo: http://dabodev.com/about There's also another rich application framework which uses PyQt and looks very good, but I forgot the name. I'm not sure about wether this is free or commercial. Thanks for reading, Alex.ander -- Alexander ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Descriptors and type declaration order
Hi guys, I've got the following (not working) code: class Attribute(object): def __init__(self, attribute_name, att_type_name): self._attribute_name = attribute_name try: self._attribute_type = globals()[att_type_name] except KeyError: self._attribute_type = getattr(globals()[__builtins__], att_type_name) def __get__(self, obj, obj_type): return getattr(obj, self._attribute_name) def __set__(self, obj, value): if isinstance(value, self._attribute_type): setattr(obj, self._attribute_name, value) else: raise ItemTypeException(self._attribute_type, type(value)) class BaseItem(object): ident = Attribute(ident, int) owner = Attribute(owner, str) item = Attribute(item, BaseItem) if __name__ == __main__: print About to create an item test = BaseItem() print OK The problem is that the descriptors are created when the module is evaluated. But at this time the class BaseItem is not known yet. Any ideas? Cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Combining two Dictionaries
def combine(d1, d2):
for key in d1:
if key in d2:
d2[key] += d1[key]
[Remark]
I usually avoid changing function arguments. But later on you're talking
about using this function as a method a class, so d1 and d2 would be
instance attributes I guess.
When I initialize the class which holds these dictionaries, though, I need
to make sure that all the keys contained in d2 match the keys of d1. Thus I
tried:
d1 = {'a': 0, 'b': 0, 'c': 0}
Now d1 holds the address of a dict in memory. The dict contains your data.
d2 = d1
Now d2 holds the same address of the same dict in memory. d1 and d2
refer to the same dictionary.
My understanding was that d2 looked at d1 once, grabbed its keys and values,
and went off to do its own thing.
You would need to use copy() explicitly.
import copy
d2 = copy.copy(d1) # swallow copy
# or a deep copy
# - copies also referenced objects recursively
# usefull if you have e.g. lists as values in your dict
# and want them copied too.
d2 = copy.deepcopy(d1)
Just as if you typed:
x = 3
y = x
x = 6
y still holds the value 3.
Python has mutable and immutable types. Str and int, for example, are
immutable. Dicts and list for example are mutable.
The statement x=6 binds x to a new object, because the object with value
3 cannot be changed.
There are a lot of explanations about mutable and immutable types. Much
better then I could. You could search the list, for example here:
http://dir.gmane.org/gmane.comp.python.tutor
or the web or see this overview in the docs:
http://docs.python.org/reference/datamodel.html#objects-values-and-types
Generally, I wouldn't copy an existing dict to make sure the other dict
has the same values. The data must come from somewhere. I would check
the data, then you wouldn't need to check the container.
Finally, you could use dict.get with a default set to 0, then you
wouldn't need to care, e.g. (using dict comprehension and creating a new
dict):
def combine_2(d1, d2):
return {key: d1[key]+d2.get(key, 0) for key in d1}
But that's a bit dirty semantic wise, better to check the input data ...
just to show you the syntax.
HTH,
Jan
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Re: [Tutor] Gtk - relational data display and edit
Am 26.04.2011 17:34, schrieb bod...@googlemail.com:
Hi,
I am reading in data from a csv file which will be in a format like this
User1, attrib1, attrib2
User2, attrib1, attrib2
Etc.
And need to display this in a window. My initial thought was to use gtk.Entry
widgets because I will need to edit this data, but I don't think this will work
as I will also need to read the data back, in relation to the user column, e.g
I will have something like
[Psuedocode]
For I in entries:
A = usercolumn
B = attrib1column
C = attrib2column
Somefunction(A,B,C)
[/psuedocode]
I don't think I could use this method with entry boxes as I have no idea how
many entries there will be (column length will be fixed) so I can't create the
entry widgets beforehand
You could use a table widget. I'm sure GTK has something like that (I'm
using Qt).
Otherwise, creating a dynamic widget for one set of your data is not
as hard as it might sound. You need to keeping references to the
composing widgets, for example in a dict. Here's some PyQt Pseudocode:
# You can retrieve the dictionary and the fieldnames with help of the
# csv module
att_name_to_value = {User: User1, Att1: attrib1, Att1: attrib1}
fieldnames = [User, Att1, Att2]
att_name_to_line_edit = {}
# This is Qt specific
layout = QtGui.QGridLayout()
for row, fieldname in enumerate(fieldnames):
label = QtGui.QLabel(fieldname)
line_edit = QtGui.QLineEdit(att_name_to_value[fieldname]
att_name_to_line_edit[fieldname] = line_edit
# add the label to the first col
layout.addWidget(label, row, 0)
# add the line_edit to the second col
layout.addWidget(line_edit, row, 1)
my_main_widget = QtGui.QWidget()
my_main_widget.setLayout(layout)
Now, if you need to read the changed data from the widget (triggered by
a button_clicked event or what ever) you can call a function to read the
data like this:
def read_data_from_widget(att_name_to_line_edit):
for att_name, line_edit in att_name_to_line_edit.items():
# do the conversion, e.g. PyQt
new_text = str(line_edit.text())
# do whatever you wish with the new data ...
HTH,
Jan
Anyone have any suggestions?
Thanks,
Bodsda
Sent from my BlackBerry® wireless device
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Re: [Tutor] counting a list of elements
Am 01.04.2011 19:16, schrieb Karim: Hello, I would like to get advice on the best practice to count elements in a list (built from scractch). It's not clear to me what your starting point is. If you don't have a list and don't need a list, but have a large number of objects you create in your code sequentially or a large number of other events and you want to know how many of those objects exist / events have occured, then simply use a counter while creating. If you have a list (for whatever reason), then use len(). HTH, Jan The number of elements is in the range 1e3 and 1e6. 1) I could create a generator and set a counter (i +=1) in the loop. 2) or simply len(mylist). I don't need the content of the list, indeed, in term of memory I don't want to wast it. But I suppose len() is optimized too (C impementation). If you have some thought to share don't hesitate. Karim ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Meta language and code generation
Am 01.04.2011 19:09, schrieb Karim: Hello All, I would to ask you if somebody has experience or can give direction in a new project I have. I have a meta language description (in xml) from which I should generate code on different languages. In my case, lisp and tcl. You need to provide more information of your description to get some specific hints. The other day a had a xml file containing a business object model with hierarchy and relations. Then I wrote a code generator to build a module with Python classes for each business item. The code generator created properties for lazily resolving relations modelled via ids in the database and stuff like that. This was very straightforeward using a simple print statements like the following: print class %s(object):\n % class_name print def __init__(self, %s) % constr_arg ... Cheers, Jan Any idea in term of design, examples, links will be appreciated! Kind Regards Karim ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] counting a list of elements
Am 01.04.2011 19:16, schrieb Karim: Hello, I would like to get advice on the best practice to count elements in a list (built from scractch). The number of elements is in the range 1e3 and 1e6. 1) I could create a generator and set a counter (i +=1) in the loop. 2) or simply len(mylist). I don't need the content of the list, indeed, in term of memory I don't want to wast it. But I suppose len() is optimized too (C impementation). If you have some thought to share don't hesitate. Just a general suggestion: Provide code examples. I know most of the times you don't have code examples yet as you're thinking of how to solve your problems. But if you post one of the possible solutions the experienced guys here will very likely direct you in the proper direction. But without code it's hard to understand what you're after. Cheers, Jan Karim ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Meta language and code generation
Am 01.04.2011 20:56, schrieb Karim: On 04/01/2011 08:29 PM, Knacktus wrote: Am 01.04.2011 19:09, schrieb Karim: Hello All, I would to ask you if somebody has experience or can give direction in a new project I have. I have a meta language description (in xml) from which I should generate code on different languages. In my case, lisp and tcl. You need to provide more information of your description to get some specific hints. The other day a had a xml file containing a business object model with hierarchy and relations. Then I wrote a code generator to build a module with Python classes for each business item. The code generator created properties for lazily resolving relations modelled via ids in the database and stuff like that. This was very straightforeward using a simple print statements like the following: print class %s(object):\n % class_name print def __init__(self, %s) % constr_arg ... Cheers, Jan In fact in xml I have something like that: A metafunction in fact kind of metfunc name=call_back_do_stuff_function parameterx/parameter parametery/parameter /metafunc I have to generate the call_back_do_stuff_function(x,y) in lisp and tcl according to a catalog of specs of what this function must do generically. I can do prints for each metafunctio I read but my concern is is there std libs to help to have good design and methodology. Is it interesting to use command module of something like that, is interesting to use a parser like pylex or pyparsing? I have 50 metafunctions in catalog for now. In fact, my point is to have a great extensive design methodology. Strategy pattern would suit? Other patterns? std modules? No ideas about patterns or standarad lib modules from my side, but a short description of how I would do it: Create an abstraction for the catalogue. That's as far as I can see the hardest part. Here you have to decide if and how to split the things your functions have to do into reusable chunks. Then create code generators for these chunks (using print statements). You can name these functions and store the references in dicts like catalog_comp_name_to_tcl_gen. If you get new functions that need new building blocks you can write new generator functions and extend your dictionaries. The generation of your tcl and lisp functions-frames should be straigt forward. You need to link the parameters to the building block generator functions you've created before. When you're done with that, you can improve the design step by step. Too me, this approach works better than thinking to much about design in advance, as often you don't see what you really need unless you've started to code. HTH, Jan Lots of question here! Regards Karim Any idea in term of design, examples, links will be appreciated! Kind Regards Karim ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] counting a list of elements
Am 01.04.2011 21:31, schrieb Karim:
On 04/01/2011 08:41 PM, Knacktus wrote:
Am 01.04.2011 19:16, schrieb Karim:
Hello,
I would like to get advice on the best practice to count elements in a
list (built from scractch).
The number of elements is in the range 1e3 and 1e6.
1) I could create a generator and set a counter (i +=1) in the loop.
2) or simply len(mylist).
I don't need the content of the list, indeed, in term of memory I don't
want to wast it. But I suppose len() is optimized too (C impementation).
If you have some thought to share don't hesitate.
Just a general suggestion: Provide code examples. I know most of the
times you don't have code examples yet as you're thinking of how to
solve your problems. But if you post one of the possible solutions the
experienced guys here will very likely direct you in the proper
direction. But without code it's hard to understand what you're after.
Cheers,
Jan
Thank you all for you answers to clarified I built a collection of
dictionnaries which represent database query on a bug tracking system:
backlog_tables , csv_backlog_table = _backlog_database(table=table,
periods=intervals_list)
backlog_tables is a dictionnary of bug info dictionnaries. The keys of
backlog_tables is a time intervall (YEAR-MONTH) as shown below:
backlog_tables= {'2011-01-01': [{'Assigned Date': datetime.date(2010,
10, 25),
'Category': 'Customer_claim',
'Date': datetime.date(2010, 10, 22),
'Duplicate Date': None,
'Fixed Reference': None,
'Headline': 'Impovement for all test',
'Identifier': '23269',
'Last Modified': datetime.date(2010, 10, 25),
'Priority': 'Low',
'Project': 'MY_PROJECT',
'Reference': 'MY_PROJECT@1.7beta2@20101006.0',
'Resolved Date': None,
'Severity': 'improvement',
'State': 'A',
'Submitter': 'Somebody'},
.
}
_backlog_database() compute the tuple backlog_tables , csv_backlog_table:
In fact csv_backlog_table is the same as backlog_tables but instead of
having
the query dictionnaries it holds only the number of query which I use to
create
a CSV file and a graph over time range.
_backlog_database() is as follow:
def _backlog_database(table=None, periods=None):
Internal function. Re-arrange database table
according to a time period. Only monthly management
is computed in this version.
@param table the database of the list of defects. Each defect is a
dictionnary with fixed keys.
@param periods the intervals list of months and the first element is the
starting date and the
the last element is the ending date in string format.
@return (periods_tables, csv_table), a tuple of periodic dictionnary
table and
the same keys dictionnary with defect numbers associated values.
if periods is None:
raise ValueError('Time interval could not be empty!')
periods_tables = {}
csv_table = {}
interval_table = []
for interval in periods:
split_date = interval.split('-')
for row in table:
if not len(split_date) == 3:
limit_date = _first_next_month_day(year=int(split_date[0]),
month=int(split_date[1]), day=1)
if row['Date'] limit_date:
if not row['Resolved Date']:
if row['State'] == 'K':
if row['Last Modified'] = limit_date:
interval_table.append(row)
elif row['State'] == 'D':
if row['Duplicate Date'] = limit_date:
interval_table.append(row)
# New, Assigned, Opened, Postponed, Forwarded, cases.
else:
interval_table.append(row)
else:
if row['Resolved Date'] = limit_date:
interval_table.append(row)
periods_tables[interval] = interval_table
csv_table[interval] = str(len(interval_table))
interval_table = []
return periods_tables, csv_table
This is not the whole function I reduce it on normal case but it shows
what I am doing.
In fact I choose to have both dictionnaries to debug my function and
analyse what's going
on. When everything will be fine I will need only the csv table (with
number per period) to create the graphs.
That's why I was asking for length computing. Honnestly, the actual
queries number is 500 (bug id) but It could be more
in other project. I was ambitious when I sais 1000 to 10
dictionnaries elements but for the whole
list of products we have internally It could be 5.
I see some similarity with my coding style (doing things by the way),
which might not be so good ;-).
With this background information I would keep the responsibilities
seperated. Your _backlog_database() function is supposed to do one
thing: Return a dictionary which holds the interval and a list of result
dicts. You could call this dict interval_to_result_tables (to indicate
that the values are lists). That's all your function should do.
Then you want to print a report. This piece of functionality needs to
know how long the lists for each dictionary entry are. Then this
print_report function should be responsible to get the information it
needs by creating it itself or calling another function, which has the
purpose to create the information. Latter would be a bit too much, as
the length would be simply be:
number_of_tables = len(interval_to_result_tables
Re: [Tutor] New person greets you all!
Am 11.03.2011 17:12, schrieb Yaşar Arabacı: Hi, First of all, I want to greet you all since this is the first time I will be using this mail groups. I consider myself being familiar with programming logic, structures in general. I do/did lots of PHP programming. I know python and PHP is pretty much different things, I am saying this just to show yourself my level of understanding on programming. I am not computer major or anything, but I am highly interested in. Today, I decided to make a chat application using python. I have chosen python because I know its powerfull and easy to use. The first step for me to go should be, clearly, begin learning how to use it :) My question is, where would you recommend for me to read tutorials, see example etc. What is the best approach would be? The official Python tutorial is a good start. You get familiar with the Python documentation as well. http://docs.python.org/py3k/ (Find the link to the tutorial on this page.) A classic and famous tutorial is here: http://www.alan-g.me.uk/ If you have any questions about this, you're lucky to be on this list, because the author of this ressource is very active here. (One of or the founder of the list?) Another classic is Dive into Python. You can find it easily with google. There're two versions, Python 2.x and 3.x. By the way, I would recommend starting with Python 3.2. Some 3rd party libs and web frameworks are not ported yet, but for your chat app you should be very happy with Python 3.2. Recently, a tutorial with a bit of a different style has been finished. I haven't done it and the style is not my cup of tea, but some people like it a lot. It's called Learning Python the hard way. Google for the url... Now, welcome to the beach of programming! Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] very odd math problem
Am 11.03.2011 04:23, schrieb Alex Hall: Hi all, I am trying to get a list of ordered pairs from the below function. In my code, evaluate is more exciting, but the evaluate here will at least let this run. The below runs fine, with one exception: somehow, it is saying that -2+2.0 is 4.x, where x is a huge decimal involving E-16 (in other words, a really tiny number). Does anyone have any idea what is going on here? You can find some great posts at a thread about decimal floating point numbers some weeks ago for background reading. Or (and) look at this: http://docs.python.org/tutorial/floatingpoint.html#floating-point-arithmetic-issues-and-limitations Now my guess is: i is calculated as a sum of floats of step 0.1. That means you have in the base 2 representation an approximation of 0.1, not exactly 0.1, but something like 0.10123123. When i reaches approximately 2.0, it is actually 2.0342374 (or what ever). On the other hand, e1 can be represented precisely if it's 2.0 in the base 2 representation. But the sum of e1 and i is actually your tiny number. That's why 2.0 - 2.0 is exactly 0.0, but (20*0.1 - 2.0 is not). To elaborate, you could add some lines to your code: def getCoords(f, e1, e2, step=.1): time=0 i=0 coords=[] while time=e2: print time=+str(e1)+++str(i)+= print type(e1) print type(i) time=e1+i time_2 = e1 + e2 print %s, %.24f % (time, time) # app 0.0 print %s, %.24f % (time_2, time_2) # exact 0.0 coords.append((time, evaluate(f, time))) i=i+1*step return coords The reason why Python prints i as 2.0 in the first print statement is probably due to some internal auto-rounding when using str(). See the last paragraph of the link above. No idea, what's exactly going on under the hood. HTH, Jan def getCoords(f, e1, e2, step=.1): #returns a list of (x,y) tuples from e1 to e2 at the given accuracy (step) time=0 i=0 coords=[] while time=e2: print time=+str(e1)+++str(i)+= time=e1+i print time #watch this line when above is -2+2.0 coords.append((time, evaluate(f, time))) i=i+1*step return coords def evaluate(x,y): return x*y ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] very odd math problem
Am 11.03.2011 06:05, schrieb Steven D'Aprano: Alex Hall wrote: Hi all, I am trying to get a list of ordered pairs from the below function. In my code, evaluate is more exciting, but the evaluate here will at least let this run. The below runs fine, with one exception: somehow, it is saying that -2+2.0 is 4.x, where x is a huge decimal involving E-16 (in other words, a really tiny number). Does anyone have any idea what is going on here? Let's reword the description of the problem... 2.0 - 2 is a really tiny number close to 4e-16 Welcome to the wonders of floating point maths! Repeat after me: Floats are not real numbers... floats are not real numbers... floats are not real numbers... everything you learned about arithmetic in school only *approximately* applies to floats. Half :) and half :( First off, anything involving e-16 isn't a huge decimal, it's a tiny decimal, very close to zero, no matter what the x is: 0.0004x Also, although you say -2 + 2.0 in a comment, that's not actually what you calculate. I know this even though I don't know what you calculate, because I can test -2 + 2.0 and see that it is exactly zero: -2 + 2.0 == 0 True Somewhere in your calculation you're probably calculating something which *looks* like 2.0 but isn't. Here's an example: x = 2 + 1e-14 print(x) 2.0 x == 2.0 False but you can see the difference by printing the float with more decimal places than shown by the default view: repr(x) '2.01' Another problem: you calculate your values by repeated addition. This is the wrong way to do it, because each addition has a tiny little error, and repeating them just compounds error upon error. Here's an example: x = 0.0 for i in range(10): ... x += 0.1 ... x == 1.0 False print(x) 1.0 repr(x) '0.99989' The right way is to do it like this: x = 0.0 for i in range(1, 11): ... x = i*0.1 ... x == 1.0 True This ensures that errors don't compound. Some further resources: http://floating-point-gui.de/ http://introcs.cs.princeton.edu/91float/ David Goldberg used to have a fantastic (although quite technical) discussion of floating point issues, What Every Computer Scientist Should Know About Floating-Point Arithmetic: http://docs.sun.com/source/806-3568/ncg_goldberg.html Unfortunately, since Oracle bought Sun, they've removed the article. Bastards. If you can find a copy of Apple's old Apple Numeric Manual (2nd Edition), it has a fantastic introduction by William Kahan. Even though the book is about Apple's SANE, a lot will apply to other floating point systems as well. Google on William Kahan and read his stuff :) Damn, you're fast!! ;-)) ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] BLAS Implementation on Python
Am 08.03.2011 20:00, schrieb Alan Gauld: Stefan Behnel stefan...@behnel.de wrote He doesn't have to write it, as it is very obvious, that no Python code on earth (even written by Guido himself ;-)) stands a chance compared to Fortran or C. Look at this: There is one big proviso. The C or Fortran needs to be well written It's seriously hard to write computational Python code that is faster than C code, though. Agreed, it was the assertion that no Python code on earth...stands a chance... that I was objecting to. There are many areas where the C code would have to be pathologically bad to be beaten by Python, but there are plenty of places where only slightly inefficient C code can be competitive relatie to Python. Maybe there're those areas, but the top posters question is about reimplementing BLAS, which is a highly optimized package for linear algebra. And in this area no pure Python code on earth on any currently available Python implementation stands a chance performance wise to one of the C or Fortran implementations. Alan G. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] BLAS Implementation on Python
Am 07.03.2011 01:50, schrieb Mahesh Narayanamurthi: Hello, I am thinking of implementing a BLAS package in pure python. I am wondering if this is a good idea. I don't think so. Usually people write extensions to the CPython implementation (when talking about performance, we need to talk about Python implementations like CPython, Jython or PyPy) in C to do high performance stuff. Pure CPython is (depeneding on the problem) magnitudes slower than C. Also, there's NumPy SciPy. Check those out. More comments below ... My design goals are: [1] Efficient manipulation of Matrices and Vectors using pure python objects and python code. No, not efficient in terms of performance. [2] Targetted to run on Python3 Good idea. NumPy and SciPy will be (are already?) ported. [3] Extensive use of defensive programming style [4] To serve as a reference design for future High Performance Code in Python The future of High Performance Python is probably PyPy. [5] To serve as a reference material in classroom courses on numerical computing or for hobbyist programmers Good idea, as Python is clear and nice to read. Thanks, Mahesh Narayanamurthi ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] BLAS Implementation on Python
Am 07.03.2011 22:44, schrieb Steven D'Aprano: On Tue, 8 Mar 2011 12:28:56 am Knacktus wrote: Am 07.03.2011 01:50, schrieb Mahesh Narayanamurthi: Hello, I am thinking of implementing a BLAS package in pure python. I am wondering if this is a good idea. Sure, why not? Even if nobody uses it, it looks good on a resume and you will hopefully learn a lot. I don't think so. Usually people write extensions to the CPython implementation (when talking about performance, we need to talk about Python implementations like CPython, Jython or PyPy) in C to do high performance stuff. Pure CPython is (depeneding on the problem) magnitudes slower than C. Typical pure Python code is between 10 and 100 times slower than C, but talking about implementations, it is the aim of the PyPy project to use Just In Time compilation and clever optimizations to meet *and exceed* the speed of static C compilers. In just a few years, with a handful of people working on it, and a tiny grant from the EU, they have already doubled the speed of CPython. If PyPy could get *half* the love and attention that CPython gets, who knows what they could accomplish? (If only Google had thrown some work into PyPy, instead of wasting time with Unladen Swallow that never went anywhere useful...) But the beauty of Python is that if a piece of code is too slow, you can rip it out into an extension written in C or Fortran while keeping the rest of the library in Python. See, for example, the re module, which has a front end written in Python and the regex engine in C. The itertools module is another good example. Using a few primitives written in C, itertools allows Python code to run efficiently and quickly. Also, there's NumPy SciPy. Check those out. More comments below ... My design goals are: [1] Efficient manipulation of Matrices and Vectors using pure python objects and python code. No, not efficient in terms of performance. How do you know how efficient his code will be before he's even written it? He doesn't have to write it, as it is very obvious, that no Python code on earth (even written by Guido himself ;-)) stands a chance compared to Fortran or C. Look at this: http://shootout.alioth.debian.org/u32/performance.php?test=spectralnorm CPython implementation runs 12 mins compared to 8 secs of a Fortran implementation. PyPy is about 100 secs, which is remarkable but still far off. [...] The future of High Performance Python is probably PyPy. Exactly why a pure-Python library *may* be useful. Today it will be slow, running under CPython, but in five (unlikely) or ten years (possibly), it may be fast, running under PyPy. Or not. Who can tell what the future will bring? ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Help!
Am 03.03.2011 22:28, schrieb Andrew Bouchot: okay so this is my comp sci lab * Problem: *ProductionTime.py It takes exactly 2 minutes and 7 second to produce an item. Unfortunately, after 143 items are produced, the fabricator must cool off for 5 minutes and 13 seconds before it can continue. Write a program that will calculate the amount of time required to manufacture a given number of items. * Output: *Output the amount of time D days HH:MM:SS * Sample Input : * numItems =1340 Represents the numbers items to be manufactured * Sample Output : * 2 days 00:03:17 this is the coding i have written for it! numitems= int(raw_input(Enter the number of items needed to be manufactured:)) seconds=numitems*127 m, s = divmod(seconds, 60) h, m = divmod(m, 60) print %d:%02d:%02d % (h, m, s) but how would i add the 5 min and 13 seconds after 143 items have been produced??? For any given number of item, how many cool-down periods do you have in total? What's the prodcution time without cooling? ---||---||--||-- producing |cooling |producing |cooling |producing |cooling |producing HTH, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] A class that instantiates conditionally ?
Am 01.03.2011 07:49, schrieb David: I have an idea that might clean up my code slightly, if I can make one of my classes clever enough to refuse to instantiate itself if a necessary condition is not met. I think that's too clever ;-). Instead, you could create a function which has the only and explicit purpose to decide wether or not to create the class, e.g. def class_for_condition(condition): if condition: return MyClass() return None and use this throughout your code, e.g. my_object = class_for_condition(condition) But to me, it sounds a bit like trouble in general. As Alan said, you have to deal with two options for my_object in the remaining code. I can't really judge without seeing what you want to do later on, but maybe you have the chance to branch on a higher abstraction level? if condition: do_all_this_stuff() # do the things with my_object else: do_the_other_stuff() # do the things you don't need my_object Cheers, Jan Below I propose some example code that seems to achieve this, and I am asking here for feedback on it, because I have not written much python. So I might be doing something unwise due to fiddling with things I don't totally understand. My aim is that instead of writing this: class MyClass: pass condition = 0 if condition: my_object = MyClass() else: my_object = None I could instead write this: class MyClass_2: # put the if-test here inside the class my_object_2 = MyClass_2(condition) to achieve the goal that (my_object_2 == None) when (condition == False). I read the (ver 2.6) Python Language Reference Section 3.4.1. Basic customization Section 3.4.3. Customizing class creation Most of the content there is way beyond my current understanding, but I came up with the following code, which seems to work: class MyClass_2(object): def __new__(self, condition): if condition: return object.__new__(self) else: return None condition = 0 my_object_2 = MyClass_2(condition) print my_object_2 condition = 1 my_object_2 = MyClass_2(condition) print my_object_2 Can anyone see any technical or style issues with that? Or alternatively reassure me that it is completely ok? Thanks. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] couchdb.mapping 'Document' class
Am 01.03.2011 16:19, schrieb Emanuel Lauria: Hi everyone, I'm trying to map a couchdb document to a python object using couchdb.mapping. I'm stuck in the very first part were it says I should declare a Python class that inherits from the 'Document'.. Where does this 'Document' superclass comes from? I can't resolve it. Or do I have to create it? How? Could someone point me in to the right direction? import couchdb class Person(Document): ... name = TextField() ... Traceback (most recent call last): File stdin, line 1, in module NameError: name 'Document' is not defined It looks like the class Document is located in the module couchdb.client (it's chapter 3.3). This should work: import couchdb.client class Person(couchdb.client.Document): ... HTH Jan Thanks for your help, and please forgive me if im too n00b in this. I havent found any documentation except http://packages.python.org/CouchDB/mapping.html which is not enough. Thanks ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Object, methods, class
Am 26.02.2011 18:49, schrieb Christopher Brookes: Hi, Is there in Python private/protected attributes in class like in other langage ? Yes, there is. But it's protected by convention not compiler ;-). Check out this: http://docs.python.org/tutorial/classes.html#private-variables -- Brookes Christopher. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Object, methods, class
Once again a very insightfull answer. Much appreciated! Same to you, Alan. I paricularly like the even longer answer. It remindes us of how lucky we are using Python and brings me light in dark times when I wish I had better code completion in my IDE for my own spaghetti-code ;-)) ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Unintentionally manipulating a list
Am 25.02.2011 15:49, schrieb ranjan das: I am facing the following problem I have a list of the form INPUT= [ [ ['A1-N','A2-Y','A3-N' ],['B1-Y','B2-N','B3-N' ] ], [.] ] and I want an output of the form (selecting only those elements which have a Y associated with them) OUTPUT=[ ['A2-Y', 'B1-Y'],[] ] I wrote the following code. Although it gives me the desired output, it CHANGES the list INPUT now after i run the code I get INPUT as the same as OUTPUT (which i dont want to happen). I have used the copy function but it still is not working. Any help or pointers is appreciated _CODE_ from copy import copy temp=copy( INPUT ) OUTPUT=temp for i in range(len(temp)): for j in range(len(temp[i])): for k in range(len(temp[i][j])): if temp[i][j][k][-1]=='Y': OUTPUT[i][j]=temp[i][j][k] There's no need for an index. You can iterate over the elements directly and create the result on the fly: results = [] for sub_list in INPUT: sub_results = [] for sub_sub_list in sub_list: sub_sub_results = [] for entry in sub_sub_list: if entry.endswith(Y): sub_sub_results.append(entry) if sub_sub_results: sub_results.append(sub_sub_results) if sub_results: results.append(sub_results) Uuppsy daisy, not really readable code ;-). Your solution looks cleaner. I bet, some of the gurus can come up with a real pythonic solution. Cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] dict['_find']
Am 20.02.2011 05:14, schrieb Max Niederhofer:
Hello all,
Hello Max,
first post, please be gentle. I'm having serious trouble finding an
alternative for the deprecated find module for dictionaries.
The code (from Zed Shaw's Hard Way, exercise 40) goes something like
this. Hope indentation survives.
cities = {'CA': 'San Francisco', 'MI': 'Detroit', 'FL': 'Jacksonville'}
I use a naming convention for dicts that has made me very happy on
several occasion ;-):
key_to_value, in your case
state_to_city = {...}
def find_city(themap, state):
if state in themap:
return themap[state]
else:
return Not found.
cities['_find'] = find_city
Did you put this entry into the same dictionary as the data on purpose?
Or is the purpose a kind of dispatch? Something that could be a dict on
its own, like
private_function_name_to_function = {'_find': find_city}
You should try to keep things seperate and explicit.
while True:
print State? (ENTER to quit),
state = raw_input( )
if not state: break
city_found = cities['_find'](cities, state)
print city_found
My question is - how do I rewrite this using an alternate module given
find is deprecated? Grateful for all suggestions or pointers. For
reference, I'm using 2.6.1 on darwin.
Thanks so much for your help.
Best,
Max
--
Dr. Maximilian Niederhofer
Founder, Qwerly
http://qwerly.com/ | http://qwerly.com/max
+44 78 3783 8227
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Re: [Tutor] scraping and saving in file
Am 29.12.2010 10:54, schrieb Tommy Kaas:
Hi,
I’m trying to learn basic web scraping and starting from scratch. I’m
using Activepython 2.6.6
I have uploaded a simple table on my web page and try to scrape it and
will save the result in a text file. I will separate the columns in the
file with #.
It works fine but besides # I also get spaces between the columns in the
text file. How do I avoid that?
This is the script:
import urllib2
from BeautifulSoup import BeautifulSoup
f = open('tabeltest.txt', 'w')
soup =
BeautifulSoup(urllib2.urlopen('http://www.kaasogmulvad.dk/unv/python/tabeltest.htm').read())
rows = soup.findAll('tr')
for tr in rows:
cols = tr.findAll('td')
print f,
cols[0].string,'#',cols[1].string,'#',cols[2].string,'#',cols[3].string
You can strip the whitespaces from the strings. I assume the
string-attribute returns a string (I don't now the API of Beautiful
Soup) E.g.:
cols[0].string.strip()
Also, you can use join() to create the complete string:
resulting_string = #.join([col.string.strip() for col in cols])
The long version without list comprehension (just for illustration,
better use list comprehension):
resulting_string = #.join([cols[0].string.strip(),
cols[1].string.strip(), cols[2].string.strip(), cols[3].string.strip(),
cols[4].string.strip()])
HTH,
Jan
f.close()
And the text file looks like this:
Kommunenr # Kommune # Region # Regionsnr
101 # København # Hovedstaden # 1084
147 # Frederiksberg # Hovedstaden # 1084
151 # Ballerup # Hovedstaden # 1084
153 # Brøndby # Hovedstaden # 1084
155 # Dragør # Hovedstaden # 1084
Thanks in advance
Tommy Kaas
Kaas Mulvad
Lykkesholms Alle 2A, 3.
1902 Frederiksberg C
Mobil: 27268818
Mail: tommy.k...@kaasogmulvad.dk mailto:tommy.k...@kaasogmulvad.dk
Web: www.kaasogmulvad.dk http://www.kaasogmulvad.dk
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Re: [Tutor] Choice of Python
Am 28.12.2010 14:41, schrieb Stefan Behnel: Abdulhakim Haliru, 28.12.2010 13:38: I come from a Cakephp, zend framework angle cutting through ASP.net,VB and C# at an intermediate level. [...] Is python really worth the pain or should I just skip it ? Given that you already invested your time into learning all of the above (which basically cover about 1 1/2 of several main corners of programming), I think you should really take some time off to unlearn some of the bad habits that these particular languages tend to teach you. Python is a truly good way to do that. My advice: don't spend too much time reading books. Pick a task that sounds like fun to implement and give it a try with Python. Some would propose exercises from project Euler for this or maybe pygame, but you'll likely have your own idea about what's fun and what isn't. +1 for jumping into coding. You seem to have enough experience in programming generally. With Python the fun comes with the experienced productivity. At least, that was the case with me. Learning the syntax is not the deal, but how to design your app. You can use the best of OO, functional and procedural programming. Also, Python is to me the best general purpose language. You can create little helper scripts, web apps and rich client apps with PyQt or WxPython. Stefan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] vim as a python editor
Am 15.12.2010 23:26, schrieb Paul Griffiths: Hi - I'm a beginner at programming and Python. I have been looking for an editor to replace Idle and tried out a few. I liked Geany but decided on vim because I am also learning Linux and the vim skills might be useful. I run Python 2.6.5 on Ubuntu 10.04. How have those of you who use vim configured it? I have looked on the web but got a bit confused by the advice and options. I am currently following some of the advice in the on-line tutorial at http://openbookproject.net/thinkcs/python/english2e/app_c.html and - installed the full version of vim (sudo apt-get install vim-gnome) - created a .vimrc file in my home directory and entered syntax enable filetype indent on set et set sw=4 set smarttab map f2 :w\|!python % - added the following to .bashrc: EDITOR=vim export EDITOR I open up a terminal in the folder where I keep my python files and create two additional tabs in this terminal. I use the first tab to run python, the second one to run vim and the third one for running linux commands such as ls to list the folder contents. Is this is a reasonable approach? Thank you for any feed back. Sure. I'm more an IDE-guy for Python now, but in my before-days with Fortran I used pretty much this approach. Even though I'm using an IDE (on Windows) myself, I would recommend learning vi/vim. Regs, Jan PaulG ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] vim as a python editor
Am 15.12.2010 23:26, schrieb Paul Griffiths: Hi - I'm a beginner at programming and Python. I have been looking for an editor to replace Idle and tried out a few. I liked Geany but decided on vim because I am also learning Linux and the vim skills might be useful. I run Python 2.6.5 on Ubuntu 10.04. How have those of you who use vim configured it? I have looked on the web but got a bit confused by the advice and options. I am currently following some of the advice in the on-line tutorial at http://openbookproject.net/thinkcs/python/english2e/app_c.html and - installed the full version of vim (sudo apt-get install vim-gnome) - created a .vimrc file in my home directory and entered syntax enable filetype indent on set et set sw=4 set smarttab map f2 :w\|!python % - added the following to .bashrc: EDITOR=vim export EDITOR I forgot: Here some more information about vim and Python: http://wiki.python.org/moin/Vim Some guy tuned vim to the maximum with code completion and everything. But start simple to learn the basics. You can extend anytime later. Jan I open up a terminal in the folder where I keep my python files and create two additional tabs in this terminal. I use the first tab to run python, the second one to run vim and the third one for running linux commands such as ls to list the folder contents. Is this is a reasonable approach? Thank you for any feed back. PaulG ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] making onthefly attributes persistent
Am 13.12.2010 23:50, schrieb Jojo Mwebaze: On Mon, Dec 13, 2010 at 8:44 PM, Alan Gauld alan.ga...@btinternet.com mailto:alan.ga...@btinternet.com wrote: Jojo Mwebaze jojo.mweb...@gmail.com mailto:jojo.mweb...@gmail.com wrote Assuming i have a class bank as below . class bank(object): def __init__(self, bal=0): self.bal = bal def deposit(self, amount): self.bal+=amount print self.bal I define a method debit - which i add to the class onthefly bank.debit = debit #I can also add an attribute owner myaccount.owner = 'jojo' My problem is how to make the added attributes, 'owner' and 'debit' persistent automatically If that's your only problem with this approach congratulations! How does your orther code know when/if these dynamic operations/data exist so as to use them? If they just assume they exist then why not just add them in the definition. Even as nulls? While Python allows you to dynamically add features to classes/objects its not something I would recommend unless you have a really good reason - not least because you bring upon yourself all sorts of problems! If you are determined to do so you can make the objects persistent using the approach I outline on my tutorial but adding a loop to cycle over the contents of dir(). But you may find that recovering the objects - especially if they have a mixed set of attribnutes - presents even more problems... IMHO This is a feature of python that should be considered unorthodox and only to be used when no other approach will work! HTH, Thanks Allan for the feedback, the idea is to write a method like store() on the object, that probably looks up all these changes and commits them into the database. Assuming you're planning to use a database with a scheme (e.g. a relational DB) you need to define your tables in advance anyway. Even if you're using a schemeless DB, where do you track which data is in it? How do you build your queries dynamically? This can become very messy. Overall, I think Alan's recommendation to avoid dynamic attribute creation is the one to follow. Please let me know where to find approach you propose in your tutorial. I read your tutorial when i was just initiated to python, a reference would be helpful to help me find the soln without hustle. Cheers -- Alan Gauld Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org mailto:Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Ressources for licensing
Am 12.12.2010 03:42, schrieb David Hutto: On Sat, Dec 11, 2010 at 9:52 AM, Knacktusknack...@googlemail.com wrote: Hi everyone, can anybody recommend a lib or some other ressources about license mechanisms of desktop applications written in python. I'm thinking of a license-key that can be used to limit the time the application can be used. I also need to exploit the usage of a license server. You probably need: def license_this(self): print touch mine license_this(self) I don't get it. Could you please explain a bit? Cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Any recommend of UML tool and UI design tool for python?
Am 12.12.2010 19:16, schrieb Alan Gauld: cajsdy caj...@gmail.com wrote Either paid or free open source is fine. I'm creating automation frame work. Idealy it includes: test plan management, test manager across windows, unix, linux, solaris and other os. UML documentation for python scripts IDE tool for python on windoes and linux UI design tool for python(best is integrated with IDE) Eclipse would be the logical choice and there are a few free UML editor plug-ins. I've tried one (can't recall the name) and although a bit clunky compared to commercoal versions it worked fine for small class and sequence diagrams. If you don't need full CASE modelling facilities someting like a drawing tool such as Dia, Visio or Smartdraw might suffice. If you want full CASE features (model validation, simulation, code generation, reverse engineering fof diagrams from code, etc) then I think you will need to pay - and probably quite a lot! I've used both Borland Together and IBM RSA. I prefer Borland although IBM produces prettier diagrams - but I found it a lot less intuitive. to use. Both come as Eclipse plugins and work with whatever version control tools Eclipse is using. There are other standalone UML tools too but it depends how much of UML you want to use. If it's only a few basic class diagrams, sequence diagrams and state diagrams then prettty much anything will do. If you need to get into the more structural aspects of UML (deployment diagrams, components, nested states, activity charts, use-cases etc) then you might want to look at paying out some money. If you're willing to pay for a CASE tool then check out Enterprise Architect from http://sparxsystems.eu/ For the massive features I think it's reasonable priced (professional edition for 165 Euro + VAT). UML-Source Code integration with Python ... I don't know if it really works. You would need to limit your code to pure OO-style. Such integration might work with Java and C# (Enterprise Architect can do this: Change code - update UML and vice versa). Nevertheless. Enterprise Architect supports Python for reverse engineering. For designing UIs: You will need another tool. It depends on your GUI toolkit. If you're planning to use PyQt as GUI toolkit (which I can only highly recommend) you're lucky. It has GUI designer, which is quite nice. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Ressources for licensing
Hi everyone, can anybody recommend a lib or some other ressources about license mechanisms of desktop applications written in python. I'm thinking of a license-key that can be used to limit the time the application can be used. I also need to exploit the usage of a license server. Cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Which non SQL Database ?
Am 04.12.2010 23:42, schrieb Jorge Biquez: Hello all. Newbie question. Sorry. As part of my process to learn python I am working on two personal applications. Both will do it fine with a simple structure of data stored in files. I now there are lot of databases around I can use but I would like to know yoor advice on what other options you would consider for the job (it is training so no pressure on performance). One application will run as a desktop one,under Windows, Linux, Macintosh, being able to update data, not much, not complex, not many records. The second application, running behind web pages, will do the same, I mean, process simple data, updating showing data. not much info, not complex. As an excersice it is more than enough I guess and will let me learn what I need for now. Talking with a friend about what he will do (he use C only) he suggest to take a look on dBase format file since it is a stable format, fast and the index structure will be fine or maybe go with BD (Berkley) database file format (I hope I understood this one correctly) . Plain files it is not an option since I would like to have option to do rapid searches. What would do you suggest to take a look? If possible available under the 3 plattforms. As a non SQL Database I can recommend MongoDB. It's a document store, which uses binary json as format. You can create secondary indexes and also perform more sophisticated queris. The main advantage from my point of view is the ease of use. Installation was a breeze and it has an easy to use python driver. Note that you need a 64-bit OS to use it with bigger data volumes (I remember 3 GB, but it's all on their website). Thanks in advance for your comments. Jorge Biquez ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Which non SQL Database ?
Am 05.12.2010 10:41, schrieb Alan Gauld: Jorge Biquez jbiq...@icsmx.com wrote Talking with a friend about what he will do (he use C only) he suggest to take a look on dBase format file since it is a stable True enough and Dabo is worth a look since it provides not only a dbase format db engine but a good GUI builder tool too. However (Berkley) database file format (I hope I understood this one correctly) . Plain files it is not an option since I would like to have option to do rapid searches. Why not use SQL? SQLlite comes with Python, is small, easy to use and if necessary can be used in-memory and as such fast. Once you have decided to go down the database route then not using SQL nowadays is a very odd decision. Its rather liike going out looking for a car that has solid types instead of pneumatics. Why would you want to? The NoSQL databases seem to be en vogue. Some big internet companies have started to use them, like Google with its Big Table. That's how I stumbled across them. There're a lot of discussions going on on the internet which is better for which use case. There're some cases where one kind of the database type is the clear winner, but most use cases can be modelled with both. My conclusion and what draw me finally to MongoDB over PostgreSQL and SQLAlqemy was: 1) Really the ease of use (from setting up the database and later when it comes to administration and scaling, which is particularly easy). MongoDB is very useful for prototyping. 2) I don't need complex transactions and the ability to perform complex, not in advanced known queries. I'd say SQL-DBs are more sophisticated but more complex to use. For the sake of learning, go with SQL. It doesn't hurt having a driver license. If you need to go to the bakery around the corner the driver license doesn't prevent you to jump on your bicycle. Cheers, Jan HTH, ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] data structures
Am 02.12.2010 02:51, schrieb Dana:
Hello,
I'm using Python to extract words from plain text files. I have a list
of words. Now I would like to convert that list to a dictionary of
features where the key is the word and the value the number of
occurrences in a group of files based on the filename (different files
correspond to different categories). What is the best way to represent
this data? When I finish I expect to have about 70 unique dictionaries
with values I plan to use in frequency distributions, etc. Should I use
globally defined dictionaries?
Depends on what else you want to do with the group of files. If you're
expecting some operations on the group's data you should create a class
to be able to add some more methods to the data. I would probably go
with a class.
class FileGroup(object):
def __init__(self, filenames):
self.filenames = filenames
self.word_to_occurrences = {}
self._populate_word_to_occurrences()
def _populate_word_to_occurrences():
for filename in filenames:
with open(filename) as fi:
# do the processing
Now you could add other meaningful data and methods to a group of files.
But also I think dictionaries can be fine. If you really only need the
dicts. You could create a function to create those.
def create_word_to_occurrences(filenames):
word_to_occurrences = {}
for filename in filenames:
with open(filename) as fi
# do the processing
return word_to_occurrences
But as I said, if in doubt I would go for the class.
Dana
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Re: [Tutor] JOB AD PROJECT
Am 21.11.2010 04:34, schrieb delegb...@dudupay.com: Hi People, I am afraid only Alan has said something to me. Is it that solution would never come or u guys are waiting to gimme the best? I agree with what Alan wrote. Your project sounds like real challenge even for experienced developers. Even for a team of experienced developers. You need both deep knowlegde of certain areas and broad knowledge of programming, databases and networking/communication. Of course you don't get the knowlegde if you don't start to develope a system. But if you start with too much and too complex things the risk is that you get stuck. There's a saying: You've got so much in your mouth that you can't chew anymore. (And you realise it only when it has happened ;-)) To avoid that risk of suddenly being buried in complexitiy and not knowing what to do and where to move next, I'd recommend to follow a step by step learning path: With your project in mind, plan 3-5 smaller projects. Each project has one of the key technologies for your final project as focus. For example: 1) Create a Django site where users can register and unregister. 2 or 3 simple web forms. Nothing more. You'll learn all the database stuff and Django basics. 2) Build a system that handles SMS communication. 3) Build some a nice html+JS websites. ... ... Then you can tackle the last and most challenging task, which is to design your overall system: Infrastructure, layers and your business-logic modules/classes. Go in small steps! That will also keep your motivation up as you get feedback after each step. HTH, Jan Please help. Sent from my BlackBerry wireless device from MTN -Original Message- From: Alan Gauldalan.ga...@btinternet.com Sender: tutor-bounces+delegbede=dudupay@python.org Date: Sat, 20 Nov 2010 09:00:52 To:tutor@python.org Subject: Re: [Tutor] JOB AD PROJECT delegb...@dudupay.com wrote I have done some extensive reading on python. i want to design a classifieds site for jobs. Have you done any extensive programming yet? Reading alone will be of limited benefit and jumping into a faurly complex web project before you have the basics mastered will be a painful experience. I'm assuming you have at least some experience of web programming in other languages for you to take such a bold step? I am taking this as my first project and would appreciate any help. I am looking in the direction of python, maybe django. The choice of tools is fine, but its a big task for a first ever Python project! HTH, ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Paper Book
Am 18.11.2010 15:31, schrieb Srinidhi Rao: Hi, Thanks for the reply guys, I would prefer a Paper Book as I don't have a kindle(amazon) and also the PDF is not so suitable out here.. (the power cuts hamper continuity :( ) @Alan, Nice website for a beginner. I glanced through your webpage and thanks for the link. I too have an Electronics background, I am only new to Python and of course OOPs... can you suggest any good books(paper) on Python. Thanks and Regards, || SRX || My first book was Learning Python from Mark Lutz. Today, I think it's a bit too long. (OK, now I have learned most of the stuff in the book). It's certainly not the wrong choice for a beginner book. And now I'm a convinced Python fan. So it must have somehow worked. Programming in Python 3 from Mark Summerfield is also nice. I've bought it recently and like it. But can't comment on how it feels reading it as a complete novice. The best book in my opinion, however *not* a beginner book, is from David Beazley: Python Essential Reference. As the name tells it's a reference, but with a lot of good recommendations and right to the point. That might be a good choice as a second book. Or you could read it in parallel to your beginner book - look up the topics you covered in the reference book. There's another good one (also for beginners): Dive into Python. There's a free edition on the web: http://diveintopython.org/ If you like it you can also by a dead tree version. (I've learned a new expression today, too ;-)) HTH, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Advantages or disadvantages on Platform?
Am 04.11.2010 20:43, schrieb Jorge Biquez: Hello all. I am newbie and studying and working hard learning python. Per your advise I am on 2.7 . I have one question for you. I can work on Windows (XP) or under Ubuntu . The advantage of using Ubuntu is that you learn how to work in a Linux/Unix environment. Most servers are using Linux/Unix based operation systems. Therefore if your goal is to develop web-apps, I would go for Ubuntu. Also, once you've set up your development environment and know how to work with your shell, working on Linux is incredible fast and fun. I used to work professionally for engineering stuff on Linux/Unix before moving to Windows. Productivity on Linux for OS operations like organising your files and quickly modifing scripts is by far higher than on Windows. Another advantage is, that there're good editors well integrated. If you have the time to learn vim, go for it. After telling you all this, I have to admit that I'm currently on a Windows 7 machine and also perfectly happy. Using an IDE makes the OS less important. Do you see any advantages or disadvantanges to be working in one or another ? My main goal , for now, is use Python for web applictions. Thanks in advance for your comments and advice. Jorge Biquez ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] mutable types
Am 02.11.2010 13:51, schrieb John:
Hello, I thought the following should end with G[1] and G[0] returning
20. Why doesn't it?
In [69]: a = 10
a is a reference to an immutable object of type int with value 10.
Somewhere in memory is an object of type int with value 10 stored. This
object cannot be changed. a is just a name that references to the
memory adress.
In [70]: G = {}
In [71]: G[0] = [a]
now, G[0] holds a reference to a mutable object of type list with an
immutable object of type int with value 10 as its content. So, your list
holds as item the memory adress of an object int with value 10. Your
list knows nothing about other names (like a), that refer to the same
adress in memory. You have handed over the object to the list (or memory
adress of the object), not the name a.
In [72]: G[1] = G[0]
In [73]: a = 20
Now, you've created a *new* immutable object of type int with value 20.
a now refers to the adress of the new integer object. a has
forgotten everything about its former reference to the object of type
int with value 10.
You have *not* changed the old object of type int with value 10. Your
list in G[0] still holds the memory adress of the first int with value 10.
In [74]: G[1]
Out[74]: [10]
In [75]: G[0]
Out[75]: [10]
??
Now, if you would keep a reference to the list you've handed over to the
dict, you could change the content of the list, as the list is mutable.
a = [10]
G = {}
G[0] = a
G[0]
[10]
a[0] = 20
G[0]
[20]
Take care of some operations that return a copy of the list:
a = a[:]
Now, a refernces to a new list, which has also one item of type in
with value 20. But it's not the same list as originally!
a[0] = 30
Changing this new list ...
G[0]
[20]
does not affect the list, we stored in the dict.
HTH,
Jan
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Re: [Tutor] pickle problem
Am 12.10.2010 19:35, schrieb Roelof Wobben: Hello, I have this code : import urllib import pickle image = urllib.URLopener() image.retrieve(http://www.pythonchallenge.com/pc/def/peak.html,banner.p; ) plaatje = open(banner.p, rb) plaatje2 = pickle.load(plaatje) But it gives this output : Traceback (most recent call last): File C:\Users\wobben\workspace\oefeningen\src\test2.py, line 7, inmodule plaatje2 = pickle.load(plaatje) File C:\Python27\lib\pickle.py, line 1378, in load return Unpickler(file).load() File C:\Python27\lib\pickle.py, line 858, in load dispatch[key](self) KeyError: '' The last error indicates that a python module (pickle.py) tried to access a dictionary (dispatch) with the key . The expected value seems to be a callable as indicated by the (self). But there's no key in it. So, probably, this module was called with improper data. If you follow up your stack trace to where the error in your code occurs, you'll see that something is wrong with unpickling the data in your plaatje file. Obviously, the data could be passed to the pickle module. So no read error on the file. What's left? There's probably an issue with the data in the file. Now, you have to know that pickling reads and writes Python objects in a certain format. That means you can only load data with pickling, which was created by pickling. Question: Is your data in banner.p properly formatted pickling data? Note: There're different formats for pickling. Check the docs or a very nice source for examples of the Python Standard lib: PyMOTW (Google first hit); there's an article about pickling among others. But first should be the standard documentation. What does this mean ? Roelof ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Hiding Superclass Methods
Am 11.10.2010 06:24, schrieb Denis Gomes: Hi Everyone, I have a basic python question. I am writing an n dimensional vector class by inheriting from the builtin python list object. I want to be able to hide the parent object's methods in the derived class instances. Why inheriting then? Another approach to reusing exisiting methods is to wrap them into your newly defined methods. Here you would not inherit from a list, but create a list in your class (composition). E.g. class MyVector(object): def __init__(self): self.data = [] def append_data(self, new_data): self.data.append(new_data) Actually I use this all the time. And I used this before I knew about inheritance. Inheritance makes sence, when you want to reuse (almost) all methods of the superclass, like in GUI toolkits, where you typically have a base widget as superclass of a all other widgets. HTH, Jan I know I can overload the method in the derived class and raise some sort of an implementation error but that is not what I had in mind. I am also not looking to use numpy. This is strictly for learning purposes. Is there a way to hide superclass methods in python? Thanks to all, Denis ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] IDE for Python
Am 07.10.2010 17:23, schrieb Juan Jose Del Toro: Dear List; In your experience what is the best IDE for Python? I'm using Wing IDE. Very good overall package. I like especially the debug probe, which is like an interactive shell in the current stack. To me it's a good balance between features and learning curve. The only thing I really miss is refactoring support. That's why I'm currently checking out PyCharm, which is about to be released (currently release candidate). It's from the company that created IntelliJ. PyCharm is in my opinion by far the most feature-rich Python IDE, looks very impressive so far. The only drawback is that it's written in Java and has a Swing GUI ;-) (ouuch, it hurts your eyes for a while but you get over it, once you discover all those wicked features ;-)). But Wing isn't excactly eye-candy either. Both are commercial, but if you code a lot it's worth it. Check out the offerings. (I think both are free for Open Source Projects.) I also tried the free PyDev (an Eclipse plugin), which is very complete as well, but I don't get along with the Eclipse world. So, check out Wing and PyCharm. Cheers, JJ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] how to extract data only after a certain condition is met
Am 06.10.2010 18:25, schrieb Eduardo Vieira: The other day I was writing a script to extract data from a file from the line where a text is found to the end of the file. The same functionality is this sed script: '1,/regexp/'d I couldn't put my head to work around this and came up with a solution using list slicing. But how can I do that? I was experimenting with a simple list and I came up with this. I wonder if I shouldn't you a while statement, but how? a = ['m', 'a', 'r', 'i', 'g', 'o', 'l', 'd'] b = True for letter in a: if letter != 'i' and b: continue elif letter == 'i': b = False else: print letter Ok. This works, but I wonder if I shouldn't you a while statement, but how? Why would you want to use a while-loop? You would need to somehow stop the iteration (by catching some EOF Exception or the like). I think it's fine to use a for-loop as you have a predefined fixed number of iterations. I think your approach is OK. Easy to understand. But what if there's a second i after the first? In your solution all i are skipped. Also, I would choose clearer names: letters = ['m', 'a', 'r', 'i', 'g', 'o', 'l', 'd', 'i', 'n', 'i', 'o'] skip_letter = True for letter in letters: if letter == 'i' and skip_letter: skip_letter = False continue # if you don't want the first occurrence of i if not skip_letter: print letter Cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] filling 2d array with zeros
Am 27.09.2010 20:29, schrieb Steven D'Aprano: On Tue, 28 Sep 2010 03:54:55 am Alex Hall wrote: Hi again everyone, I have a 2d array (I guess it is technically a list) which I want to fill with zeros. Later I will change some values, but any I do not change have to be zeros. I have two complex for loops, but I tried to scale things down to a couple list comprehensions and I broke things. What is wrong with the following line? self.am=[[(a,b) for a in range(len(self.lines)) a=0] for b in range(len(self.lines)) b=0] Start with a single row, of n columns: [0 for i in range(n)] # the loop variable i is not used Now all you need is to set n appropriately: n = len(self.lines) [0 for i in range(n)] Is there an easier way? Yes, you don't even need a list comp: [0]*n Now make m rows of the same: [ [0]*n for i in range(m) ] And you are done. You might be tempted to take a short-cut: [ [0]*n ]*m but this doesn't work as you expect. This is one of the rare Python gotchas -- it looks like it should work, but it doesn't behave like you might expect. Try it and see: a = [[0]*3]*4 a [[0, 0, 0], [0, 0, 0], [0, 0, 0], [0, 0, 0]] a[0][1] = 2 a [[0, 2, 0], [0, 2, 0], [0, 2, 0], [0, 2, 0]] What's going on here? It's a little complicated, so let's start with a simpler situation: b = [0, 0, 0] c = b # c is an alias to the same list as b d = b # so is d e = c # and e b[0] = 3 e [3, 0, 0] Because both b and e refer to the same list (not copies!) any change to b *must* also change e. It's like if Barack Obama gets a haircut, so does the current President of the USA, because they're the same person. Now stick them in a list: a = [b, c, d, e] a [[3, 0, 0], [3, 0, 0], [3, 0, 0], [3, 0, 0]] a[0][1] = 4 a [[3, 4, 0], [3, 4, 0], [3, 4, 0], [3, 4, 0]] Modify one, modify them all, because in fact they are actually all the same list. [ [0]*3 ]*4 behaves the same way. There's no problem in the inner list, but the outer list doesn't make four copies of [0,0,0], it has *one* list repeated four times. Modify one, modify them all. Another extremly helpful explanation for every learner watching the mailing list. Steven, you really deserve the golden tutor medal of honor! Cheers, Jan P.S.: You other guys are awesome as well. Amazing mailing list... ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Python And reading the Web - Javascript
Any ideas in general in how to do this appreciated. i don't mind reading so if you have some good links they are appreciated. I have no experience myself with this task, but I would look at those resource: 1) For reading html pages in addition to the standard-lib modules: http://www.crummy.com/software/BeautifulSoup/ 2) For more advanced stuff it might be worth looking at a webkit implementation of Qt via PyQt Bindings: http://doc.trolltech.com/4.7/qtwebkit.html here the Python bindings http://www.riverbankcomputing.co.uk/news HTH, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Best practice for API design handeling collections and single objects
Hi all, I've got a question for you about how to best design an API that has to handle requests for single objects and collections of those objects. My naming conventions are: Plural nouns for collections, singular nouns for single objects. Key_to_value-style for dictionaries. So I normaly know in my code wether I'm handling collections, dicts or single types. So, here's an simplified example: #--- class Meals(object): def __init__(self, id_on_menu_to_meal): self.id_on_menu_to_meal = id_on_menu_to_meal #--- Now I need to return one meal by one id_on_menu and also several meals by several ids_on_menu. I can think of three options: 1) create two methods: #--- def get_meal_by_ident(self, ident): return self.id_on_menu_to_meal[ident] def get_meals_by_idents(self, idents): return [self.get_meal_by_ident(ident) for ident in idents] #--- 2) create one method, which is smart enough to discriminate between the input (having fun with the naming conventions ;-)): #--- def get_meal_or_meals_by_ident_or_idents(self, ident_or_idents): try: return self.id_on_menu_to_meal[ident_or_idents] except KeyError: return [self.id_on_menu_to_meal[ident] for ident in ident_or_idents] #--- 3) handle by convention application-wide only collections: #--- def get_meals_by_idents(self, idents): return [self.id_on_menu_to_meal[ident] for ident in idents] #--- Without having too much experience on things like that, my gut feeling tells me to use option 1). What would you guys consider as a best practice here? Thanks in advance and cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Can this be done easly
Am 19.09.2010 10:49, schrieb Roelof Wobben: Hello, I have this programm : class Point: def __init__(self, x=0, y=0): self.x = x self.y = y class Rectangle(Point): def _init_(self, width=0, length=0): self.width = width self.length = length You're inheriting the Point Class, but you don't initialise it. For some detailled description of inheritance in Python I rather suggest to check out some tutorials instead of trying to explain it. Also, others on this list can do this probably better. Here's one reference: http://diveintopython.org/object_oriented_framework/index.html But now some remarks regarding your problem: First, I would not consider a Rectangle as a special Point. It's not a relation like a Sportscar is a Car (is-a-relationship). It's more a relation a Rectangle has 4 Points (has-a-relationship), or 1 Point and a width and length. So, it's probably better to express your Rectangle class like this: class Rectangle(object): def __init__(self, base_point, width=0, length=0): self.base_point = base_point self.width = width self.length = length then you go (with German names ;-)): punkt = Point(3,4) rechteck = Rectangle(punkt,20,30) In your Rectangle class, the __init__ method takes only two arguments (not counting the instance: self), but you're passing three arguments. At the beginning, the error messages are a bit confusing, because they count the instance as one of the arguments. So it tells you, that you have given 4 arguments, but you might wonder Hey, I gave you 3. HTH, Jan punt = Point(3,4) rechthoek = Rectangle (punt,20,30) Now I wonder how I can change this to rechthoek = rectangle (punt,20,20) This one gives as error message : Traceback (most recent call last): File C:\Users\wobben\workspace\oefeningen\src\test.py, line 12, inmodule rechthoek = Rectangle (punt,20,30) TypeError: __init__() takes at most 3 arguments (4 given) Roelof ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] What are singletons good for?
Hey all, the usual explanation for the usage of a Singleton goes like this: Use a singleton if you want to make sure, that only one instance of a class exists. But now I ask myself: Why should I call the constructor of a class more than once if I only want one instance? After all, I decide in my code when to create an instance or when to pass an existing instance around. Example in pseudocode: class Session(object): Hold a dictionary of ident_to_data_objects def __init__(self, ident_to_data): self.ident_to_data = ident_to_data Now, that would be a typical singleton use case. I want one instance of this class application-wide. For example in a View class: class View(object): Create fancy views def __init__(self, session): self.session = session In my code I use these classes like this: class MainApp(object): Do some stuff with the data_objects def __init__(self): self.session = Session() self.view = View(self.session) Would a singleton usage in the View class look like that? class View(object): Create fancy views def __init__(self): self.session = Session() What's the point? Is it the spared typing when instanciating a lot of View classes (I wouldn't need to pass the session to the constructor). Or are there some more advantages (instead of passing the same instance aorund)? Also, what would you guys consider as disadvantages? Another question related to this topic is, if I would use a module as a singleton (as suggested by Steve and other), how would I import it the instances of a class? Maybe like this? class View(object): Create fancy views import session def do_something(self, ident): self.certain_data_object = session.ident_to_data[ident] A lot of questions, so thanks in advance for any comments! Cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] selecting elements from dictionary
xdic
{11135457: [1], 11135492: [1], 11135913: [1], 11135436: [1, 2],
11135699: [1, 2], 11135702: [1, 3], 11135901: [1]}
I want to print only those items that have [1,2] and [1,3] in any order,
such as [1,2] or [2,1], [3,1] or [1,3]
for item in xdic.keys():
... if [1,2] in xdic[item]:
... print item
You can loop over the values directly:
xdic = {11135457: [1], 11135492: [1], 11135913: [1], 11135436: [1, 2],
11135699: [1, 2], 11135702: [1, 3], 11135901: [1]}
for values in xdic.values():
if len(values) == 2:
print values
or if you only want values which contain 1 and 2 or 3:
for values in xdic.values():
if 1 in values and 2 in values or 3 in values:
print values
or a combination of the above, where you check the length and the
content of the list.
HTH,
Jan
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Re: [Tutor] design question
Am 10.09.2010 16:11, schrieb Albert-Jan Roskam: Hi Jan, Here's a screendump of my program: http://nl.tinypic.com/r/2qtlojc/7 . This might make my description a little bit clearer. The beautiful sunset will in reality be a dull, handwritten form. ;-) Regarding the iterator pattern, I was referring to this: http://www.suttoncourtenay.org.uk/duncan/accu/pythonpatterns.html#iterators-and-generators Inside my program I have to keep a list of all the image files that are scheduled for data entry. The main purpose is to be able to read in the image files one by one. Another one of the purposes of this list is to show some information on the title bar. Currently, my program only has a 'next' button and the fact that implementing a 'previous' button is causing problems suggests to me that I have to look for a more fundamentally better solution. Sounds to me that the easiest solution would be to simply use a list to hold the images, a reference to the current image and your desired methods in a class. class ImageStack(object): def __init__(self, images=None) self.images = images or [] self.current_image = None def next_image(self): if self.current_image: current_index = self.images.index(self.current_image) try: next_image = self.images[current_index + 1] except IndexError: print All images done # or return the first one else: next_image = self.images[0] self.current_image = next_image return next_image def prev_image(self): if self.current_image: current_index = self.images.index(self.current_image) try: prev_image = self.images[current_index - 1] self.current_image = next_image return next_image except IndexError: print There's no prev image print There's no current image You could also track the current_index instead of the current_image. That would make the class easier, but how to track the current image depends on what other methods you need. HTH, Jan Cheers!! Albert-Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] What Design Pattern for Document class (NOT URGENT)
Hi Karim, it's difficult to comment as to me the problem is not quite clear. But I try ;-) You have a complex xml and need to read different data types. For each type you have certain rules, how to extract them from the xml (docrules). You could create a DocRule class, that do nothing but hold instructions of how to read and write the xml for each data, e.g. xpathes. For each data type you create an instance of that class. Then, in your main xml Reader class you define a method, that accepts a doc rule instance as argument. doc_rule_1 = DocRule(some_pattern) doc_rule_2 = DocRule(another_pattern) class Reader(object): def __init__(self, filename): ... # create the etree def get_data_by_doc_rule(self, doc_rule): ... # search the tree based on the doc_rule ... # you can use any type here if it has the correct mehtods In your get_data_by_doc_rule method you can use any type for the doc_rule, that has corresponding attributes and methods (duck typing). So you have a lot of flexibility of how to create your doc_rules. Is that what you're looking for? Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] changing list index start
Am 11.09.2010 15:46, schrieb Joel Goldstick:
On Sat, Sep 11, 2010 at 9:25 AM, Rance Hall ran...@gmail.com
mailto:ran...@gmail.com wrote:
On Fri, Sep 10, 2010 at 6:14 PM, Lie Ryan lie.1...@gmail.com
mailto:lie.1...@gmail.com wrote:
On 09/11/10 07:36, Rance Hall wrote:
snip
In most cases in Python, you would almost never need to reference the
list's index directly since python makes it easy to use iterators;
however in your particular case, which is a valid exception,
enumerate()
takes an optional second argument `start` which defines the
number that
enumerate start to count with, i.e. you can do:
for i, option in enumerate(mainmenuoptions, 1):
print('%s. %s' % (i, option))
php provided a way to change this, but I can find no documentation
that says python can do this as well.
Thanks everyone for responding, Because this menu structure is
repeated many times in my code, the ideal solution would have been to
set index start = 1 in the beginning of the script.
something like sysctl variables in Linux perhaps but in this case only
valid for this program.
Its clear from the responses that this solution is not available in
python, I wish it were, it would make my life much easier for this
project.
I like the approach that Lie suggested, as it seems more natural
python to me as opposed to a workaround.
However this is also only half a solution since it applies to the
printed menus only and not to the response afterward.
It might be more trouble than its worth, but you could use a dictionary:
Instead of this:
mainmenuoptions = ['Clients','Jobs','Billing','Quotes','To Do
Items','Employee','Exit']
do this:
mainmenuoptions = {'Clients': 1,'Jobs': 2,'Billing': 3,'Quotes':
4,'To Do
Items': 5,'Employee': 6,'Exit': 7}
Use the phrases as key, and the value as your numeric index. Or you could
reverse {1: 'Clients', ...
if that suites your already written code.
If you use this pattern in many places, could you not refactor so that
you call
the process with the menu data structures as parameters, and fix the code
in a single place?
+1 for the dictionary. A variation of Joels suggestion might be:
shortcuts_to_name_and_functions = {1: ['Clients', clientsmenu], 2:
['Jobs', jobsmenu]}
for shortcut, name_and_func in shortcuts_to_name_and_functions.items():
print %s. %s % (shortcut, name_and_func[0])
# later make your call
shortcuts_to_name_and_functions[mainchoice][1]()
It seems that Luke is right looks like we have to do math with the
indexes.
Lie also referred to my particular case as a valid exception, are
there enough other such valid exceptions that requesting a feature
enhancement would gain some traction?
If this is but one of a few special cases, I doubt it would be worth
the time or trouble to formally make the request.
Maybe I should ask if there is a better way to do what I want to do
here. Is there?
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--
Joel Goldstick
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Re: [Tutor] design question
Am 10.09.2010 11:23, schrieb Albert-Jan Roskam: Hi, I've made a small data entry program where a picture of a hand-written, scanned form is shown next to several text entries. The design has been largely 'bottom up', although of course I started with a rough sketch. I started with the following classes: Menu (responsible for the widget creation), Autocomplete (a subclass of the tkinter text entry widget which I've found on the internet, I wanted to keep this intact), Convert (responsible for the conversion/cropping of the images, which is somewhat tedious) and Events (here's the pain spot: this has become a mixed bag). Originally, the Events class was supposed to contain all the commands behind the widgets, but it has slowly gotten more responsibilities. Notably, all methods that deal with reading/writing the data also live here. The program is about 500 lines of code now, including blanks. It's difficult to judge from the outside. It sounds to me like a good idea to create separate classes or modules for reading and writing. I'd like to rewrite to entire program so that (1) all classes have just one responsibility (2) classes connect to as little other classes (so it becomes easy to e.g. change to another widget set). I'd love to hear some thoughts or advice on the new design from you (I hope my description wasn't too short). Is there a specific design pattern that could be used? One specific, additional question: the program has a title bar that shows something like processing file X (1 of 3; 33%). My colleague suggested to use the Iterator pattern (gang of four) for this. Is this (a) overkill (b) a simple opportunity to apply this pattern? For what exactly do you want to use the pattern? The iterator pattern is easy to implement in Python. And the usage of iterators is even more easy (you can use them in loops without calling the next() method explicitly). Lists among others are iterator types. You can create your own with generator functions or of course implement the iterator-protocol. See here: http://docs.python.org/library/stdtypes.html#iterator-types Generally iterator types and generators are great features of Python. For a more concrete advice you'd need to explain a bit further what you need to do. HTH Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Conditional attribute access / key access
The sizes given are in bytes. So 200,000 instances of this class, plus the list to hold them, would take approximately 34 megabytes. An entry level PC these days has 1000 megabytes of memory. Huge? Not even close. The items hold a lot of metadata, which I didn't provide in my example. Depending on the source up to 30 addional attributes per item, mainly strings. And I will have several sources. So far there're no restrictions about how to model the items. They can be dicts, objects of a custom class (preferable with __slots__) or namedTuple. Those items have references to each other using ids. That approach sounds slow and ponderous to me. Why don't you just give items direct references to each other, instead of indirect using ids? Unfortunately I have to able to use a relational database later on. Currently I'm using a document database for developement. That's where the ids are coming from and you're right: They are a pain ... ;-) If you *need* indirection, say because you are keeping the data in a database and you want to only lazily load it when needed, rather than all at once, then the right approach is probably a proxy object: class PartProxy(object): def __init__(self, database_id): self._info = None self.database_id = database_id @property def info(self): if self._info is None: self._info = get_from_database(self.database_id) return self._info That's it! Excactly what I was looking for! That eases the id-pain. Thanks!! Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Conditional attribute access / key access
Hey everyone,
I have a huge number of data items coming from a database. So far
there're no restrictions about how to model the items. They can be
dicts, objects of a custom class (preferable with __slots__) or namedTuple.
Those items have references to each other using ids. Fresh from the
database the items look like this (using dicts as examples):
item_1 = {id: 1, name: root, children_ids: [2, 3]}
item_2 = {id: 2, name: child_1, children_ids: [4]}
item_3 = {id: 3, name: child_2, children_ids: [6, 7, 8]}
Now I'd like to resolve the references on demand. For that purpose I
think about adding another entry in my dicts (children_obj_refs):
item_1 = {id = 1, name = root, children_ids = [2, 3],
children_obj_refs = [item_2, item_3]}
To achieve that substitution dynamically on demand I could use a function:
def get_children(item):
try:
return item[children_obj_refs]
except AttributeError:
# pseudocode for retrieving items from db based on ids
fresh_items_from_db = get_items_from_db(item[children_ids])
# Now create new dict entry for future usage
item[children_obj_refs] = fresh_items_from_db
However, I dislike to have to call a function all the time. I'd rather
get this done under the hood when accessing the dict with
item[children_obj_refs]. So I've looked into subclassing a dict and
overwriting the __getitem__() method like this:
class TestSubDict(dict):
def __getitem__(self, key):
try:
return self[key]
except KeyError:
# load item from db and so on ...
But I run into recursion limit problems.
Any recommendations about that? (I'm not restricted to dicts, custom
classes are OK to, but with __slots__ to limit memory consumption.)
Many thanks in advance and cheers,
Jan
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Re: [Tutor] Conditional attribute access / key access
Am 30.08.2010 17:53, schrieb Francesco Loffredo:
Two questions and one doubt for you:
1- How many generations do you want to keep in a single item (call it
dictionary or list, or record, whatever)? I mean, what if some children
have children too, and some of those have more children, etc ?
There's always one level (generation) of children in an item. An item
can have zero or more direct children. And a lot of grandchildren and
grandgrandchildren etc. The item-structure represent an assembly
hierarchy of the parts of a car. So overall the structure can be up to
about 20 levels deep and consist of up to 20 items overall, where
the application needs to handle several structures.
2- Are you SURE that there are no circular references in your database?
In your example, what if item_3 was
item_3 = {id: 3, name: child_2, children_ids: [6, 1, 8]}? Is't
it possible that those recursion limit problems you had could come from
some circular reference in your data?
That's a good hint. But the recursion limit doesn't come from that (the
test data actually had no children. I used a single instance of my dict.)
d- If the number of data items is really huge, are you sure that you
want to keep the whole family in memory at the same time? It depends on
the answer you gave to my question #1, of course, but if retrieving an
item from your database is quick as it should be, you could use a query
to resolve the references on demand, and you wouldn't need a special
structure to hold the rest of the family. If the retrieval is slow or
difficult, then the creation of your structure could take a significant
amount of time.
One thing is, that I have to do some additional calculations when
resolving the structure. The items will get some kind of
labels/conditions and versions, further, when resolving the structure a
set of rules for those conditions is given. At my first shot I'll have
to do those calculations in the Python code (even if it would be very
wicked to do stuff like that with SQL). So, I will always have a large
number of items in memory, as I don't want to call the database for each
structure-level I want to expand. Also, I'm using a pyqt-treeview
(AbstractItemModel) for a client-site gui. For this purpose I need to
create an additional structure, as in the original data items can have
more than one parent, which is not permitted in the model for the treeview.
The whole idea of replacing the id-references to object-references is to
enhance performance and make the application code easier.
Thanks for the feedback so far.
Hope this helps,
Francesco
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Re: [Tutor] Help with Object Oriented Programming
Am 30.08.2010 20:13, schrieb Tino Dai: Hi Everybody, I'm beefing up my Object-Oriented Analysis and Design - getting the gaps in my knowledge filled in through the Head First OOAD book (http://headfirstlabs.com/books/hfooad/). That book focuses on Java - is there a comparable book for Python? I have already read the Alan Gauld's intro on classes, but I'm looking for more. My goal is to be able to design and code in Python in an OO fashion exploiting the OO paradigm as it related to Python at the level of Kent Johnston (hey, if I'm going to dream, might as well dream big! :) ). Currently, some of the things such as inheritance and encapsulation apply across OO languages but interfaces (I know that Zope has this) and mixin's are language specific constructs. If anybody could point me in the right direction, that would be great! TIA, Tino ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor Hi Tino, I've started in a very simliar fashion. My first OO-app was a procedural Fortran-style Java application ;-) Then I stumbled over Python but was aware that I had no clue about OO-Programming. I read the book Head First OOAD, too. And also stuff about design patterns. At the beginning, it's a bit confusing. There's a lot of overhead involved due to Java's static typing. You have to use inheritance, interfaces, abstract classes etc. to achieve certain things, e.g. make code general (develop for interface not implementation ...) With Python the same things can be achieved a loot easier and in the end clearer (at least to me). One example are the iterator and visitor patterns. Those can be done so smoothly in Python thanks to everything is a first class object. It would be fatal to try to translate Java Code from the DP book to python. Overall, Java OO and DP are helpful to know and understanding the ideas behind them will help you with Python. But things are done differently with Pyhton (don't try to mimick Java!) and you will be very very happy about that. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Help with Object Oriented Programming
You could google for 1) Alex Martelli, Design Patterns He's a Pyton guru and there're some online talks (at Google and some conferences) about DP; a bit difficult to understand, well, he's guru ;-) 2) http://www.suttoncourtenay.org.uk/duncan/accu/pythonpatterns.html I like that one. Also, there're some presentations about the lack of design patterns in Python on the web. Google should help or look at the PyCon archives. Very useful stuff there. And finally, 1 gramm of practice weighs more than 1 ton of theory. I see it right now after some month absence from coding. Cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] type() problem
fruit=ramadana print fruit heeft als type, type(fruit) y=len(fruit) print y z=fruit[:3] print z These lines put in a module and executed print (using Python 2.7): fruit heeft als type type 'str' 8 ram Strange that it doesn't work for you. I can only advice you to check the file again or run the code from the Python shell. HTH, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Elementtree and pretty printing in Python 2.7
Hi guys, I'm using Python 2.7 and the ElementTree standard-lib to write some xml. My output xml has no line breaks! So, it looks like that: ItemsProject creation_date=heute//Items instead of something like this: Items Project creation_date=heute/ /Items I'm aware of lxml which seems to have a pretty print option, but I would prefer to use the standard-lib ElementTree which seems not to have a feature like this. Do I miss something using the ElementTree-lib or is it bug? Cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Done -- Elementtree and pretty printing in Python 2.7
Hi guys, just found hidden in the Schema change in Etree-Thread the answer to my formatting question: Quotation: ElementTree doesn't have a way of formatting (pretty printing) XML files, so there can't be that many newline characters in the structure (they may be in the occur, though!). There's a pretty printing recipe on the effbot site that you can easily adapt to inject the newline characters you need. The recipe works fine. Cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Error Using exec to Run Module Files
Am 18.08.2010 06:54, schrieb mes...@juno.com:
I'm a rank beginner in Python. Took advantage of the O'Reilly one-day sale of
'Learning Python' announced on the tutor, and starting to work my way through
it. When I tried out an example from pg57, on Using exec to Run Module Files,
I get the following result:
exec(open('script1.py').read())
Traceback (most recent call last):
File stdin, line 1, inmodule
File string, line 1
%!PS-Adobe-3.0
^
SyntaxError: invalid syntax
It looks like the first line of your file script1.py contains
%!PS-Adobe-3.0. (Which is no valid syntax, of course)
Have you doublechecked the content of script1.py and does it work by
invoking it form the command line with python script1.py? My guess is
the file somehow got screwed up.
HTH
Jan
What is going on/
Gene R.
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[Tutor] Multiple inheritance for mixin attributes
Hello everyone, I've got a question about class design. I want to model classes like these (examples): # class BaseItem(object): def __init__(self, ident, name, description): self.ident = ident self.name = name self.description = description class DataSourceItem(object): def __init__(self, ident, name, description, data_source): self.ident = ident self.name = name self.description = description self.data_source = data_source class BaseItemCollection(list): def __init__(self, ident, name, description): self.ident = ident self.name = name self.description = description def default_version(self): return self[-1] class BaseDataSourceItemCollection(list): def __init__(self, ident, name, description, data_source): self.ident = ident self.name = name self.description = description self.data_source = data_source def default_version(self): return self[-1] ### Now, to remove all the duplicated code I could use inheritance. But that would lead to multiple inheritance and the question how to initialise both superclasses? I would appreciate some advice about how to model classes like this. Personaly, I don't have to use inheritance, but I have no better idea. Would you accept at least some duplication to avoid multiple inheritance? Thanks in advance, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Performance list vs. deque for [-1]
Hi everyone, I'm wondering what's the fastet datatype in python to lookup the last element in an ordered collection. I know about lists, of course, and read about deques. As I understand deques have better performance for popping and adding elements, but I didn't understand what's the behavior for look-up's without any changes to the collection. I will not pop() out of my ordered collection, and only recently append. Also, the collections will be small (about 10-20 elements), but I will have huge amount (5-10) of those collections which need to be processed for certain tasks in my application. Thanks in advance and cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] how to get str() to use my function?
Am 04.08.2010 17:37, schrieb Alex Hall: It worked, thanks. Is there a list of these functions somewhere? That is, the functions that map implicitly to operators or implied uses? For example, printing will call __str__, as will a cal to str(). What about math or comparison operators? I have heard of __eq__, __gt__, and so on, but I tried to implement one and I got an error saying that it required three arguments. It did, but only because the first was self. I put the function inside my card class: def __eq__(self, card1, card2): return(card1.rank==card2.rank) #end def __eq__ For some reason it is still looking for three arguments... The official list of all special methods can be found at the datamodel description, chapter 3.4: http://docs.python.org/reference/datamodel.html#special-method-names Most Python books also have some explanations about this. Maybe the nice online book Dive into Python has a chapter? (I didn't check...) Regarding your problem: I've flew very fast over the docs. __eq__ seems to expect two arguments (self, other). So probably your method of the card class should look like: def __eq__(self, card2): return(self.rank==card2.rank) Cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Python and Abaqus
Am 30.07.2010 13:44, schrieb leo.ruggier...@libero.it: Dear All, I am trying to have access to the Abaqus kernel by a Python script. My intention is to avoid to use the Abaqus GUI (or command line) to run a simulation. The idea is to lunch the Python script by DOS or Python module. The problem is that my Python script runs from the Abaqus command line or from the GUI (menu--file--run script) but it doesn't run from outside. Without knowing very much about the Abaqus command line my guess is that a special environment (env. variables, path, etc.) is set up for the Abaqus command line. In that case you need to create that environment in your DOS command window where the python script is to run or create that environment within your python script (see the os module in the standard library). But prior to that you need to know more about the environment. You could query the Abaqus command line (if it's a DOS window by invoking the python shell then using os.environ, if it's a Python you can use os.environ directly after importing os, of course). Alternatively you could examine the command file, *.bat file or whatever opens the Abaqus command shell. Probably that file has a lot of set up stuff in it. HTH and cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Question
~So is it better to learn 1 programming language first, then learn another. Or better to pretty much learn them at the same time? And why? First, I think python is a bit underrated for creating real applications. I'm amazed again and again by it's power on all programming scales (e.g. quick and dirty csv-file hacks, medium scripts to bigger app with gui (e.g. pyqt is unbelievable powerful) and database-connections). So, I hardly see something of an urge for learning c++. Python will bring you a looong way. Then, I think when learning to programm, there're two big levels. Level one is to learn the language syntax, basic algorithms, data types, etc.. The second level is how to design larger programs. How to make them as easy and clear to understand (and to maintain) as possible. You'll find yourself thinking about what to place where in the code, read stuff about OO-Programming and Design Patterns etc.. I'm currently at this level. So, if you start learning another language, it will broaden your level 1 skills, but I think it'll be more valuable to become better at level 2. So, once you're familiar with python, I would start creating some bigger apps. One thing to keep in mind is that python has a lot of patterns build in due to its dynamic typing and first class callables. A lot of things can be expressed much easier with python than with Java or C++. That will leave you more brain power for innovation. But for the pure sake of learning design patterns, Java might be a candidate. Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] How to model objects aimed to persistence?
Hi everyone, within a python application I can easily model object association with simple references, e.g.: # class FavoritMovies(object): def __init__(self, movies): self.movies = movies class Movie(object): def __init__(self, name, actor): self.name = name self.actor = actor gladiator = Movie(Gladiator, Russel Crowe) my_favorit_movies = FavoritMovies([gladiator]) kung_fu_panda = Movie(Kung Fu Panda, Jack Black) your_favorit_movies = FavoritMovies([gladiator, kung_fu_panda]) ## So far, so good. But what is best practise to prepare this data for general persistence? It should be usable for serialisation to xml or storing to an RDBMS or ObjectDatabase ... I guess I have to incorporate some kind of id for every object and use this as reference with some kind of look-up dictionary, but I wouldn't like it and hope that there're some other sweet pythonic solutions? Cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] How to model objects aimed to persistence?
Am 17.06.2010 02:17, schrieb Alan Gauld: Steven D'Aprano st...@pearwood.info wrote Deliberate misspellings in class and variable names will cost you *far* more in debugging time when you forget to misspell the words than they will save you in typing. Trust me on this. Thanks for that hint. I can imagine the nightmares ... It was just a spelling mistake. English is not my native language and I sometime tend to skip trailing es ;-). But I think I need to clarify my question a bit. The point I'm unsure with is how to best model references in python for persistence when not using pickle or any dedicated python. Python doesn't even need names as reference to the objects location in memory. I could do something like this: ### my_favourite_movies = FavouriteMovies([Movie(Gladiator, Russel Crowe)]) ### When I want to rebuild the data from a xml file or database, my objects somehow need to know which references to other objects they hold. I don't now wether I have to use explicit indices in my python code to make it xml-ready and if that's the case, how to do it smoothly. Or whether there's some other trick. Cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] What's the catch with ZopeDB?
Hey everyone, I'm planning to create small application which manages product data e.g. parts of cars. There are quite some relations, e.g. - a car consists of certain assemblies, - an assembly consists of certatin parts, - a part has serveral documents which describe the part, e.g. a CAD document or material data. So, one could think of storing the data in a relational database. But now I start to think ... ;-): - I would just need some predefined queries which would be performed by Python code, of course. Maybe using an ORM. - Therefore, I don't think I need all the power and flexibility of SQL. - I will work with Python objects. Why should I translate to an relational schema just for persistence? - Performancewise, caching is probably much more sensitive than pure database performance. (That my guess...) To me, ZopeDB (a object database for Python) looks like an awesomely easy solution. I could save some brain power for the innovative part or drink more beer watching the soccer world cup. At the same moment, I wonder why anyone in the python world would go through the hassle of using relational databases unless forced. So, has anyone experience with ZopeDB? Are there some drawbacks I should be aware of before getting a book and dive in? (It sounds too good ;-)) Cheers, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Unit testing command-line options from argparse or optparse
Am 18.05.2010 22:49, schrieb Serdar Tumgoren: Hello all, Does anyone have advice for writing unit tests against variables set by command-line options? I have a program I'd like to run in either debug or live mode, with various settings associated with each. Below is some pseudo-code that shows what I'd like to do: snipped argparse import and options setup mode = p.parse_args() #always set to either --debug or --live if mode.live: recipients = ['jsm...@email.com mailto:jsm...@email.com', 'jane...@email.com mailto:jane...@email.com'] # set logging to a file elif mode.debug: recipients = ['ad...@admin.com mailto:ad...@admin.com'] # log to stdout The live and debug attributes are set by command-line flags passed to the argparse module. What I'd like to do is write tests that check whether various settings (recipients, logging, etc.) are configured properly based on the command-line options. But if mode is not set until runtime, I clearly can't import it into my suite of unit tests, right? Is there some standard testing approach to this problem (perhaps mocking?) that you all can recommend? I'd greatly appreciate it. Serdar ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor I just had a look at the optparse documentation ... huuu, quite heavier than I have expected But to your question: You could reorganise your main module. Put all your code which is on module level into a function called main with mode as argurment and add the neat if __name__ == __main__ condition at the end of your module to parse the command line options and call your main function. When you import your module to your test, you have to call the main function manually and can pass a mock for the mode as required. Let's say your main module is called serdars_main_module serdars_main_module.py: -- def main(mode): # all the program logic if mode.live: recipients = ['jsm...@email.com mailto:jsm...@email.com', 'jane...@email.com mailto:jane...@email.com'] # set logging to a file elif mode.debug: recipients = ['ad...@admin.com mailto:ad...@admin.com'] # log to stdout # ... if __name__ == __main__: mode = p.parse_args() #always set to either --debug or --liv main(mode) # Then your test module could look like: serdars_test_module.py: - # import serdars_main_module import unittest class ArgParseMock(object): def __init__(self, live, debug): self.live = live self.debug = debug class TestDebugMode(unittest.TestCase): def test_live_mode(self): mode = ArgParseMock(True, False) # create the mock for the arguments serdars_main_module.main(mode) # call the main logic with the mock # def test_debug_mode(self): mode = ArgParseMock(False, True) # create the mock for the arguments serdars_main_module.main(mode) # call the main logic with the mock # ## Hope that helps, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] pickle.load() all dict
Am 16.05.2010 09:10, schrieb Yutao Deng:
Hi all:
I'm trying to learn to use Python wrote a applet to record every day
doing.
and i use the pickle
pickle.dump something to file no problem i think.
but pickle.load whith a problem. can not load all dict do my way that
what i pickle.dump().
My code:
import cPickle as pickle
pickle_file = open(data2,rb)
i = pickle.load(pickle_file)
print i
i = pickle.load(pickle_file)
print i
i = pickle.load(pickle_file)
print i
i = pickle.load(pickle_file)
print i
i = pickle.load(pickle_file)
print i
console show :
{'2010-5-23': ['1242', 'first']}
{'2010-5-24': ['1232', 'third']}
{'2010-5-25': ['211', 'second']}
{'2010-3-22': ['3211', 'fou']}
{'2050-3-2': ['3990', '322']}
This is i want but that's silly. if the dict too much, then i have not
ideas.
the other way from
http://mail.python.org/pipermail/tutor/2005-July/039859.html
import cPickle as pickle
pickle_file = open(data2,rb)
number_of_pickles = pickle.load(pickle_file)
for n in range(number_of_pickles):
p = pickle.load(pickle_file)
print p
this way didnt work for me.
console show:
Traceback (most recent call last):
number_of_pickles = pickle.load(pickle_file)
cPickle.UnpicklingError: invalid load key, '
'.
how do i define a range for pickle.load a file . i mean that how can i
know how many dict in the data2.
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If you want to unpickle a file which contains an unknown number of
pickled objects, this should work. You'll get a list containing all the
objects.
#
import cPickle
import pprint
test_data_1 = {2010-12-13: [1324, first]}
test_data_2 = {2010-12-14: [234, first_and_a_half]}
test_data_3 = {2010-12-15: [132224, second]}
for data in (test_data_1, test_data_2, test_data_3):
with open(data2.pickle, ab) as file_stream:
cPickle.dump(data, file_stream, 2)
with open(data2.pickle, rb) as file_stream:
pickled_objects = []
while True:
try:
pickled_objects.append(cPickle.load(file_stream))
except EOFError:
break
print Number of pickled objects is %s. % len(pickled_objects)
pprint.pprint(pickled_objects)
Cheers,
Jan
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Re: [Tutor] pickle.load() all dict
Am 16.05.2010 14:45, schrieb Yutao Deng: LOL, try...except is a good idea. i fix it lick this: with open(data2.pickle,rb) as file_stream: c = 0 while True: try: i = cPickle.load(file_stream) print i c += 1 except: print Numer of pickled objects is %s. %c break # ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor Just a remark on your except statement: You should not use except: without specifying a concrete exception class, because all kind of exceptions are then handled by the except block (and therefore hidden). If for example an IOError occurs while reading the file (for what ever reason...), it would be handled by your except block and you would never know that there was a problem reading the file. If you use except EOFError: the exception block is evaluated only when the EOFError occurs. All other exceptions are raised as usual. Best regards, Jan ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
