[Tutor] MySQLdb.converters.escape() type error
Hi, after upgrading to MySQL 5 and MySQLdb 1.2.1_p2, I have the following problem: self.db=MySQLdb.connect(host=host, user=user, passwd=passwd, db=db, cursorclass=MySQLdb.cursors.DictCursor) stringel = 'Some string' stringel = self.db.escape(stringel) File ./test.py, line 12, in ? stringel = self.db.escape(stringel) TypeError: no default type converter defined I checked the documentation for MySQLdb.converters and saw that the escape() function takes a dictionary as an obligatory second argument. This is odd, because I have always been using escape(string) without a problem. The changes in MySQLdb 1.2.1_p2 list: Mapped a lot of new 4.1 and 5.0 error codes to Python exceptions Could someone point me to the problem in the MySQL side? Thanks in advance! - Jan -- Any technology which is distinguishable from magic is insufficiently advanced. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Webprogramming with the MVC pattern
Hi, I am about to build my first web application using the MVC pattern. Now I am wondering which might be the best way to initialize both a model and a presenter based on the model and its state. My controller should look like this: # model = Models.ModelFactory(cgi_parameters) view = Views.ViewFactory(model) view.Display() # The factory method ModelFactory would check the parameters and return an appropriate model: def ModelFactory(params): valid_models = dict(location=Location, prices=Prices, booking=Booking) return valid_models[params['type']](**params) class Location: ... class Prices: ... class Booking: ... But I am stuck with the ViewFactory method. Since the appropriate view depends on both the model's class (type) and state, I am not sure how to implement this. I could do it the ugly way: def ViewFactory(model): if (model.__class__ == 'Booking' and model.state == 'new'): view = new NewBooking() elsif (model.__class__ == 'Booking' and model.state == 'review'): view = new BookingReview() ... return view class LocationView: ... class NewBooking: ... class BookingReview: ... class BookingConfirmation: ... But there must be a better way. Could you give me a hint? Thanks, Jan -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] XSLT module
Hi, I intend to use an XSLT processor, and found various modules (4suite, Sab-Pyth) on the web. Could anyone recommend a specific module for transforming XML files? Thanks, Jan -- It's overkill, of course. But you can never have too much overkill. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Exception repeated in a loop
Hi, I use the following loop to parse some HTML code: for record in data: try: parser.feed(record['content']) except HTMLParseError, (msg): print !!!Parsing error in, record['page_id'], : , msg Now after HTMLParser encounters a parse error in one record, it repeats to execute the except statement for all following records - why is that? !!!Parsing error in 8832 : bad end tag: '/em b', at line 56568, column 1647999 !!!Parsing error in 8833 : bad end tag: '/em b', at line 56568, column 1651394 !!!Parsing error in 8834 : bad end tag: '/em b', at line 56568, column 1654789 !!!Parsing error in 8835 : bad end tag: '/em b', at line 56568, column 1658184 Thanks. Jan -- Hanlon's Razor: Never attribute to malice that which can be adequately explained by stupidity. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Exception repeated in a loop
Hi Pawel, Pawel Kraszewski wrote on 06.12.2005: Dnia wtorek, 6 grudnia 2005 16:29, Jan Eden napisa?: Hi, I use the following loop to parse some HTML code: for record in data: try: parser.feed(record['content']) except HTMLParseError, (msg): print !!!Parsing error in, record['page_id'], : , msg Now after HTMLParser encounters a parse error in one record, it repeats to execute the except statement for all following records - why is that? Short answer: because you told Python to do so... Long answer: My hint for students having such problems is to execute their code with a pencil on a hardcopy. They read aloud what the program currently does - usually they spot the error during the first reading. Your code being read loud 1. begin loop 2. attempt to execute parser.feed 3. abort attempt if it fails, showing the error 4. take next loop So - you take next loop regardless of the failure or not. There are two ways out of here. I wrote them aloud, to transcribe into python as an excersize: (Notice the difference between this and your original) I) 1. attempt to 2. begin loop 3. abort attempt if it fails, showing the error 4. take next loop II) 1. begin loop 2. attempt to execute parser.feed 3. abort attempt if it fails, showing the error AND breaking the loop 4. take next loop Thanks, I tested your suggestion, which works fine. But I don't understand the problem with my original code. If the parser raises an exception for a certain record, it should print the error message and move on to the next record in the loop. Why would I need the break statement? What's more - if the break statement is executed, all following records will never be parsed. I still don't understand why failure of a single record affects the other records. Thanks, Jan -- There's no place like ~/ ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Exception repeated in a loop
Hi, Nelson, Scott wrote on 06.12.2005: An unhandled exception immediately stops the execution of your code. A handled exception (try/except) does not stop code execution (unless you explicitly tell it to). This shows how a handled exception does not stop code execution: try: raise Exception except: print 'caught exception' print 'fell through' This is exactly what I need Python to do: Raise the exception for a certain record and go on with the following records. I just do not see why the same loop is raised over and over again - obviously because of the same malformed HTML tag. Adding a break statement causes Python to skip all following records, which is not what I need. Thanks, Jan -- There are two major products that come out of Berkeley: LSD and UNIX. We don't believe this to be a coincidence. - Jeremy S. Anderson ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Exception repeated in a loop
Kent Johnson wrote on 06.12.2005: The parser processes up to the error. It never recovers from the error. HTMLParser has an internal buffer and buffer pointer that is never advanced when an error is detected; each time you call feed() it tries to parse the remaining data and gets the same error again. Take a look at HTMLParser.goahead() in Lib/HTMLParser.py if you are interested in the details. Aha! That's what I needed to know. Thanks to all who answered. - Jan -- I'd never join any club that would have the likes of me as a member. - Groucho Marx ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Malformed CSV
Hi,
I need to parse a CSV file using the csv module:
hotel,9,463,95,1.00
hotels,7,033,73,1.04
hotels hamburg,2,312,73,3.16
hotel hamburg,2,708,42,1.55
Hotels,2,854,41,1.44
hotel berlin,2,614,31,1.19
The idea is to use each single keyword (field 1) as a dictionary key and sum up
the clicks (field 2) and transactions (field 3):
try:
keywords[keyword]['clicks'] += clicks
keywords[keyword]['transactions'] += transactions
# if the keyword has not been found yet...
except KeyError:
keywords[keyword] = { 'clicks' : clicks, 'transactions' :
transactions }
Unfortunately, the quote characters are not properly escaped within fields:
hotel,hamburg,1,0,0
hotel,billig, in berlin tegel,1,0,0
hotel+wien,1,0,0
hotel+nürnberg,1,0,0
hotel+london,1,0,0
hotel budapest billig,1,0,0
which leads to the following output (example):
hotel9,463hamburgbillig951 in berlin tegel
As you can see, Python added 'hamburg' and 'billig' to the first 'hotel'
row's click value (9,463), and '1' as well as ' in berlin tegel' to the
transactions (95). I am aware that I need to convert real clicks/transactions
to integers before adding them, but I first wanted to sort out the parsing
problem.
Is there a way to deal with the incorrect quoting automatically?
Thanks,
Jan
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Re: [Tutor] Malformed CSV
Kent Johnson wrote on 02.12.2005:
I'm not entirely sure how you want to interpret the data above. One
possibility is to just change the double to single before
processing with csv. For example:
# data is the raw data from the whole file
data = '''hotel,hamburg,1,0,0
hotel,billig, in berlin tegel,1,0,0
hotel+wien,1,0,0
hotel+nurnberg,1,0,0
hotel+london,1,0,0
hotel budapest billig,1,0,0'''
data = data.replace('', '')
data = data.splitlines()
import csv
for line in csv.reader(data):
print line
Output is
['hotel,hamburg', '1', '0', '0']
['hotel,billig, in berlin tegel', '1', '0', '0']
['hotel+wien', '1', '0', '0']
['hotel+nurnberg', '1', '0', '0']
['hotel+london', '1', '0', '0']
['hotel budapest billig', '1', '0', '0']
which looks pretty reasonable except for the last line, and I don't
really know what you would consider correct there.
Exactly, the last line is the problem. With correct (Excel-style) quoting, it
would look like this
hotel budapest billig,1,0,0
i.e. each quote within a field would be doubled, and the output would be
['hotel budapest billig', '1', '0', '0']
i.e. the quoting of the original search string
hotel budapest billig
would be preserved (and this is important). I guess I need to notify the
engineer responsible for the CSV output and have the quoting corrected.
Thanks,
Jan
--
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Programming Perl
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Re: [Tutor] Malformed CSV
Kent Johnson wrote on 02.12.2005: Jan Eden wrote: I guess I need to notify the engineer responsible for the CSV output and have the quoting corrected. If that is possible it is a much better solution. I hate to hack around bad data - much better to correct the source of the data if possible. Right. In fact you may have little choice if you want to use the CSV module - for example what if the first field has commas and quotes? Could you have a line like this? hotel, budapest, billig,1,0,0 [...] BTW do you really have doubled quotes in all the hotel fields, or just the one with quotes? The data in your original post is inconsistent. Yes, and that's the source of my problem: The data is based on user input to Google, which tends to be extremely inconsistent. Users seem to use any kind of absurd quoting, like hotel miami miami,hotel Thanks again, Jan -- Life's unfair - but root password helps! ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Dynamic inheritance?
Hi,
Kent Johnson wrote on 20.11.2005:
Use getattr() to access attributes by name. SiteA is an attribute of
Templates and Page is an attribute of SiteA so you can get use
getattr() twice to get what you want:
site = getattr(Templates, self.site_name) self.template =
getattr(site, self.template_type)
Unfortunately, this does not seem to work if Templates is a package, not a
module. Python complains:
AttributeError: 'module' object has no attribute 'SiteA'
args = ('module' object has no attribute 'SiteA',)
even though there is a module SiteA within package Templates. When manually
importing SiteA from Templates, everything is good.
From your previous message, I read that modules are treated just like classes
or any other attribute - did I misinterpret your advice?
Thanks,
Jan
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Re: [Tutor] Dynamic inheritance?
Hi,
Jan Eden wrote on 22.11.2005:
Hi,
Kent Johnson wrote on 20.11.2005:
Use getattr() to access attributes by name. SiteA is an attribute
of Templates and Page is an attribute of SiteA so you can get use
getattr() twice to get what you want:
site = getattr(Templates, self.site_name) self.template =
getattr(site, self.template_type)
Unfortunately, this does not seem to work if Templates is a package,
not a module. Python complains:
AttributeError: 'module' object has no attribute 'SiteA'
args = ('module' object has no attribute 'SiteA',)
even though there is a module SiteA within package Templates. When
manually importing SiteA from Templates, everything is good.
Found a solution:
import Templates
#...
def GetTemplates(self):
__import__('Templates.', globals(), locals(), [self.identifier])
site = getattr(Templates, self.identifier)
self.template = getattr(site, self.template_type)
works.
Thanks,
Jan
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Re: [Tutor] Dynamic inheritance?
Kent Johnson wrote on 20.11.2005: Use getattr() to access attributes by name. SiteA is an attribute of Templates and Page is an attribute of SiteA so you can get use getattr() twice to get what you want: site = getattr(Templates, self.site_name) self.template = getattr(site, self.template_type) Thank you! I did not take into account that modules and classes can be treated just like data attributes. - Jan -- Remember: use logout to logout. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Dynamic inheritance?
Hi, I have a number of classes, each of which should inherit from a related superclass in another module: class A(Super.A): ... class B(Super.B): ... class C(Super.C): ... Is there a way to dynamically determine the value of Super at runtime? Background: Depending on certain object attributes which are set during the object initialization, I need to use a different set of templates for the respective object. Example: If a page object belongs to site A, it needs to inherit from the template class SiteA.Page, a gallery object belonging to site B should inherit from SiteB.Gallery etc. The problem is that the template classes are not self contained, i.e. SiteB.Gallery inherits from SiteB.List, SiteB.Base etc. Thanks in advance, Jan -- Any sufficiently advanced technology is insufficiently documented. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Dynamic inheritance?
Hi Kent, Kent Johnson wrote on 19.11.2005: Jan Eden wrote: Is there a way to dynamically determine the value of Super at runtime? Background: Depending on certain object attributes which are set during the object initialization, I need to use a different set of templates for the respective object. Sure, just import the correct template module conditionally and give it a new name: if site == 'siteA': import SiteA as Super else import SiteB as Super class A(Super.A): etc. If you need to do the import based on a string use the __import__() function: http://www.python.org/doc/current/lib/built-in-funcs.html Excellent. This is exactly what I need. I was not aware of the fact that you can rename modules upon importing them. The problem is that the template classes are not self contained, i.e. SiteB.Gallery inherits from SiteB.List, SiteB.Base etc. Thanks in advance, I don't see why that is a problem? Please disregard the last statement in my first message: There is indeed no problem with this requirement. Thanks for your help, Jan -- Common sense is what tells you that the world is flat. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Dynamic inheritance?
Kent Johnson wrote on 19.11.2005: Danny Yoo wrote: Here's a small example that shows how classes can be treated just like any other value in Python: # def makeYa(superclass): class Ya(superclass): def sayHi(self): superclass.sayHi(self) print ya return Ya class ValleyPerson: def sayHi(self): print like, so, oh my gosh, hi? FrankensteinClass = makeYa(ValleyPerson) instance = FrankensteinClass() instance.sayHi() # Yeah, that'll work too :-) Or even def makeAB(moduleContainingSuperClass): class A(moduleContainingSuperClass.A): pass class B(moduleContainingSuperClass.B) pass return A, B A, B = makeAB(siteA) So there's no need to do trickery with conditional imports; Python treats classes as first-class objects that can be passed around. Trickery? ;) It's just using modules as first-class objects that are bound to names same as anything else. Which solution is better depends on whether you want to choose at the module level or with finer control. Hm, sounds like there's more than one way to do it. ;-) Thanks a lot for your examples. I hate to confess that I incorrectly described my requirements. It turns out that I am better off with a (variant of the) state design pattern. But I am stuck there, too. The situation is this: For every object, two string attributes are determined during initialization (one being read from a database, the other inherited as a superclass attribute). The first contains the site name, the second the object type. I'd like to set the template attribute to the proper class: import Templates self.site_name = 'SiteA' self.template_type = 'Page' self.template = ??? self.template should refer to Templates.SiteA.Page in this case (where SiteA is a module of package Templates, and Page is a class within that module). Danny already said that classes can be treated just like any other object - but how do I get from a string to a class or module name? Thanks for all your help, and sorry for my ignorance, Jan -- Any sufficiently advanced technology is indistinguishable from a Perl script. - Programming Perl ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Class attributes not overriding parameters
Hi, I use the following construction to make sure the data attribute site_id is set only once for each object: def GetSiteID(self): return self._site_id def SetSiteID(self, value): if not (hasattr(self, '_site_id') and self._site_id): self._site_id = value site_id = property(GetSiteID, SetSiteID) site_id is supposed to be set either through a parameter, derived from the server name (the default case) or via a class attribute: class SiteList(Lists): site_id = 1 The latter case does not work: the site_id is still derived from the server name for objects of class SiteList. Why is that? How can I make Python check the superclasses for a class attribute before applying the SiteMode() method? Thanks, Jan -- How many Microsoft engineers does it take to screw in a lightbulb? None. They just redefine dark as the new standard. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Subclassing data attributes
Hi, the module Data.py stores a number of data attributes. I'd like to structure the storage of these attributes, either in subclasses or in dictionaries. My first attempt was this: class A: templates['attr1'] = 'string' queries['children'] = ... class B(A): templates['attr2'] = 4 queries['children'] = ... class C(B): templates['attr3'] = 939.121 queries['populate'] = ... Python obviously complains about unknown names 'templates' and 'queries'. So I thought about realizing this with classes: class A: class Templates: attr1 = 'string' ... The problem here is that once an object uses class C.Templates to lookup attr3, it will not consult class A.Templates for attr1. How can I avoid a complete inheritance mess and structure all my data attributes at the same time? Thanks, Jan -- I'd never join any club that would have the likes of me as a member. - Groucho Marx ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Newbie Question - Python vs Perl
Hi Scott, Scott Clausen wrote on 30.10.2005: As a newbie to Python I'd like to know if someone can tell me some strengths and weaknesses of this language. The reason I'm asking is a friend told me I should learn Perl over Python as it's more prevalent. I'm going to be using it on a Mac. I'd appreciate hearing any views on this topic. My own view is that it's always good to learn new things as you then have more tools to use in your daily programming. I started learning Python approx. 4 months ago. I had been using Perl for about 4 years at that time. (BTW, I work on a Mac, too) The motivation for trying Python came when a certain project needed an OOP overhaul. While I was able to code an OOP version of the program, the result was rather slow and ugly. This was only partly because of my own deficiencies - Perl does not really invite you to produce clean code on larger projects (IMHO). When I re-coded the very same project in Python, I achieved a much better (faster, more readable) result within weeks. Most comparisons of Perl and Python also highlight Python's cleaner syntax, I can second that (although I got used to Perl's @$% syntax after a while). Cheers, Jan -- Common sense is what tells you that the world is flat. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Transforming object into subclass instance
Hi, my program uses an initial switch statement to create an object: valid_types = dict( pages=Show.Page, syndicated=Show.Syndicated, authors=Show.Author, author_list=Show.AuthorList, galleries=Show.Gallery, pictures=Show.Picture, slideshow=Show.SlidePicture, tex=Show.Tex, blogs=Show.Blog, blogentries=Show.BlogEntry, search=Show.Search, search_author=Show.SearchAuthor, not_found=Show.NotFound ) # ... code ommitted... page = valid_types[type]]() For a certain class, it is only during the execution of the __ini__ method that I can distinguish between two subtypes (subclasses). The subclasses define two different versions of method A. Now my question is: How can I turn an object of class X into an object of either class Y or Z while (retaining all the attributes defined so far). I know I could solve the problem by using another switch statement - but is there consistent OOP solution for this problem? Thanks, Jan -- Hanlon's Razor: Never attribute to malice that which can be adequately explained by stupidity. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] New-style classes
Hi, after updating a program to use new-style classes, I am a bit confused. My setup looks like this (simplified): #Show.py import Data class Base(object): ... class Page(Data.Page, Base): ... class Author(Data.Author, Base): ... #Data.py class Base: ... class Page(Base): ... class Author(Base): ... The module Show.py provides methods, Data.py provides data attributes. I use the property method in Data.Base for a certain attribute - but why does this work? Data.Base has no base classes, so it is not based on a built-in type: How can it be a new-style class? Thanks for any hints, Jan -- There are 10 kinds of people: those who understand binary, and those who don't ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] New-style classes
Hi Kent, Kent Johnson wrote on 29.09.2005: Data.Base has no base classes, so it is not based on a built-in type: How can it be a new-style class? Data.Base is not a new-style class, but the classes in Show are. And properties may appear to work in old-style classes. This document http://www.python.org/2.2.3/descrintro.html#property says, Properties do not work for classic classes, but you don't get a clear error when you try this. Your get method will be called, so it appears to work, but upon attribute assignment, a classic class instance will simply set the value in its __dict__ without calling the property's set method, and after that, the property's get method won't be called either. Thanks for your quick reply. I read the document you mentioned before, that's why I was confused. My actual code looks like this: class Base: def GetOwnType(self): try: return self._own_type except: return self.child_type def SetOwnType(self, value): self._own_type = value own_type = property(GetOwnType, SetOwnType) For some of the subclasses of Base, the attribute own_type is defined, the others should use child_type. For both groups of subclasses, this works fine - if own_type has not been set somewhere else, self.child_type is returned when calling self.own_type. When checking Data.Base.__mro__, I get an error, so it is not a new-style class by itself. On the other hand, every time I use the own_type attribute, I do so via instances of new-style classes (Show.Page, Show.Author etc). Could it be that the nature of these classes makes the code in Data.Base behave according to the new-style rules? Thanks, Jan -- I'd never join any club that would have the likes of me as a member. - Groucho Marx ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Simulating case statement
Hi, I used to use an extended if...elif sequence to instantiate an object and call this object's display method afterwards: if safe['type'] == pages: page = Show.Page(id=safe['id'], start=safe['start'] ...), elif safe['type'] == pages: author = Show.Author(id=safe['id']...) ... page.Display() To improve readability, I changed this code to use a dictionary: valid_types = dict( pages=Show.Page, authors=Show.Author, ... ) page = valid_types[safe_parameters['type']](safe_parameters) page.Display() The problem is that the __init__ methods of the respective classes take a different number of parameters - this is why I pass the whole safe_parameters dictionary. This has a number of drawbacks when instantiating an object in other situations because I cannot use a default for some parameters while passing some others. So I'd like to do pass the parameters individually, based on the class. I know I would need to expand the valid_types dictionary to include the parameters - but how can I pass these one by one? What I came up with is a monster (which does not work anyway): valid_types = dict( pages=dict(klasse=Show.Page, parameters=dict(id=safe['id'], start=safe['start'] ...)) authors=dict(klasse=Show.Author, ...) ... ) page = valid_types[safe_parameters['type']]['klasse'](valid_types['parameters']) page.Display() How can I circumvent the if...elif sequence and have the parameters passed individually at the same time? Thanks for any suggestions, Jan -- Common sense is what tells you that the world is flat. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Simulating case statement
Kent Johnson wrote on 27.09.2005: Jan Eden wrote: The problem is that the __init__ methods of the respective classes take a different number of parameters - this is why I pass the whole safe_parameters dictionary. I think if you pass the dictionary as keyword arguments rather than as a single dict you will get what you want. page = valid_types[safe_parameters['type']](**safe_parameters) This syntax means, use safe_parameters to populate the keyword arguments of the function. Any parameters which are not in safe_parameters will be set to their default values, and in other calls you can set the parameters as you like. Here is a simple example: I see. I did not know that I can use a formal parameter **param in calls - thought I could only do so in function definitions: def func(**param): ... func(id=1, stuff='blah') Thanks for that! Jan -- Mac OS X. Because making Unix user-friendly is easier than debugging Windows. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] __getattr__ causes TypeError
Hi,
I experienced a strange side effect using a custom __getattr__ method.
For a certain attribute, I'd like to return the value of another attribute if
the former is not present. So I wrote:
def __getattr__(self, attrname):
if attrname == 'own_type': return self.child_type
else: AttributeError, attrname
But if I include this in my base class, I get a TypeError somewhere else:
File /Users/jan/Sites/janeden/cgi-bin/Pythonsite/Show.py, line 24, in
Populate
self.page_head = re.sub('%%author%%', self.first_name+' '+self.last_name,
self.page_head)
TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'
How can this possibly be related? I am clueless.
Best,
Jan
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[Tutor] Using superclass __init__ method
Hi, I just noticed that in the following environment: class Base: def __init__(self): ... class Child(Base): pass the following statement: child = Child() would automatically execute the superclass __init__ method. This is exactly what I was looking for - but in the Cookbook, I found several suggestions on how to actively force the invocation of the superclass __init__. Is this behvaiour documented? Thanks, Jan -- There are 10 kinds of people: those who understand binary, and those who don't ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Using superclass __init__ method
Kent Johnson wrote on 22.09.2005: This is standard behavior for any class attribute - if it's not defined in the derived class, the base class is checked. It's not special for __init__. I can't find a comprehensive reference for the way attribute lookup works - anyone else? Well, I did know that any attribute used explicitly with a class instance is looked up in the class, then the base class etc: class Base: variable = 1 class Child(Base): pass child = Child() print child.variable 1 What I did not know was that the __init__ method behaves the same way - i.e. that Python looks for __init__ upon instantiation until it finds one. Thanks, Jan -- A good programmer is someone who looks both ways before crossing a one-way street. - Doug Linder ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Using superclass __init__ method
Hi, paul brian wrote on 22.09.2005: class Base: def __init__(self): print hello class Child(Base): def __init__(self): Base.__init__(self) This is how I did it so far. But in my program, I have 10 subclasses with identical __init__ methods, so I can simplify the setup a lot. Thanks for your help, Jan -- Alcohol and calculus don't mix - PLEASE don't drink and derive. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] List of class instances
Hi, I'd like to form a list of class instances. The following does not work (TextfieldLong, Textarea, TextfieldShort etc being class names): fields = [ TextfieldLong(name='title', label='Seitentitel', value=''), Textarea(name='content', label='Inhalt', value=''), ShortField(name='mother_id', label='MotherID', value=1) ] Is there a way to create such a list? Thanks in advance, Jan -- Any sufficiently advanced technology is indistinguishable from a Perl script. - Programming Perl ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] List of class instances
Hi, Jan Eden wrote on 20.09.2005: Hi, I'd like to form a list of class instances. The following does not work (TextfieldLong, Textarea, TextfieldShort etc being class names): fields = [ TextfieldLong(name='title', label='Seitentitel', value=''), Textarea(name='content', label='Inhalt', value=''), ShortField(name='mother_id', label='MotherID', value=1) ] Just found that it *does* work, but that I have to define the classes above the list assignment. Why is that? Why would Python not find the classes within the same file? TIA, Jan -- Life's unfair - but root password helps! ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] List of class instances
Hi, Orri Ganel wrote on 20.09.2005: As a side-note, unless you're okay with only being able to access those instance variables through the fields list (ie fields[0], fields[1], fields[2]), you may want to actually name them first. Yes, I am fine with that - I actually prefer to have a sorted list instead of a dictionary. I'll always access them like for field in fields: ... Thanks, Jan -- I'd never join any club that would have the likes of me as a member. - Groucho Marx ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] mod_python on OS X
Hi Danny, Danny Yoo wrote on 05.09.2005: On Mon, 5 Sep 2005, Jan Eden wrote: [Sat Sep 03 23:01:52 2005] [notice] child pid 2334 exit signal Bus error (10) [Sat Sep 03 23:01:53 2005] [notice] child pid 2333 exit signal Bus error (10) It looks that you have a locally customized verison of Python on your system. (As far as I know, Apple doesn't package Python 2.4 yet) Did you make sure to install mod_python by using that customized Python, rather than the system default? I did. The folks on the mod_python mailing list will probably know more about this, so I'd strongly recommend asking them: Yes, it is probably the best thing to do, but I wanted to avoid getting involved with yet another mailing list. *sigh* Many thanks, Jan -- Unix is user friendly - it's just picky about it's friends. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] PYTHON????
[EMAIL PROTECTED] wrote on 29.08.2005: Dear Python, How does a calculator multiply? I want to create a computer software that can multiply. How do I program the computer to multiply? Could this be a spammer aiming at mailing lists? - Jan -- The day Microsoft makes something that doesn't suck is the day they start selling vacuum cleaners. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Instance attribute as a parameter's default value
Hi, Jan Eden wrote on 26.08.2005: Hi, I need to use an instance attribute as the default value for a parameter to a method. This obviously won't work: page.Children() def Children(self, id=self.id, level=2): How can I get the id parameter to use the attribute page.id? I know I could simply use the method call page.Children(id=page.id) but I thought it is much more elegant to use a default value here. Is it possible? Addition: I do use def Children(self, id=0, level=2): if not id: id = self.id right now. But still - there has to be a smarter way. Thanks, Jan -- Any sufficiently advanced technology is insufficiently documented. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Default class in module
Hi Kent, Kent Johnson wrote on 11.08.2005: I don't know of any way to do exactly what you ask. However you can use the __init__.py module of the package to promote classes to package level visibility. Nice - that's a good start. Thank you, Jan -- Common sense is what tells you that the world is flat. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Untainting CGI parameters
Hi Kent, hi Alan,
Kent Johnson wrote on 10.08.2005:
OK, I don't know much Perl but I don't think these two snippets do
the same thing. For one thing the regexes are different, second in
the Python you need to check if the match succeeds.
my $type = ($parameters{type} ($parameters{type} =~ /^(\w+)$/)) ?
$1 : 'page';
Ok, you got me - the regexes were indeed not identical, and only the Perl code
included a check if the match was successful.
Alan G wrote on 10.08.2005:
I would like to untaint all parameters with which my CGI script is
called. Example:
Can you explain 'untaint'??? Not a term I'm familiar with...
Untainting CGI parameters is derived from Perl's taint mode - turning on this
mode makes Perl assume that all input coming from the user of a script is
probably evil and needs to be hand-checked before using it for anything outside
the script itself (e.g. calling external programs, removing files, sending mail
etc.)
if parameters.has_key('type'): match = re.search('\w+',
parameters['type'].value) type = match.group() else: type = 'page'
I Python it's better to ask forgiveness than permission so...
try: type = re.search('\w+', parameters['type'].value).group() except
KeyError: type = 'page'
Thank you - that wraps up two lines in one, just as I intended to. I tried it
before but most have mixed up something when calling the group() method on the
object returned by the search method immediately.
I will combine Kent's and your suggestion, because he included a check for an
AttributeError:
try:
type = re.search('\w+', parameters['type'].value).group() except
except KeyError, AttributeError:
type = 'page'
Thank you both,
Jan
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Re: [Tutor] Untainting CGI parameters
Hi Alan,
Alan G wrote on 11.08.2005:
I will combine Kent's and your suggestion, because he included a
check for an AttributeError:
OK, as a slightly more perl-ish solution to the no Attribute problem
you could also do this:
try:
type = re.search('\w+', parameters['type'].value).group() or
'page'
except KeyError:
type = 'page'
Are you sure?
a = 'abcd'
import re
type = re.search('\d+',a).group() or 'page'
Traceback (most recent call last):
File stdin, line 1, in ?
AttributeError: 'NoneType' object has no attribute 'group'
If the search does not succeed, the returned object has the value None, which
has no attribute group.
Thanks,
Jan
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[Tutor] Untainting CGI parameters
Hi,
I would like to untaint all parameters with which my CGI script is called.
Example:
if parameters.has_key('type'):
match = re.search('\w+', parameters['type'].value)
type = match.group()
else: type = 'page'
In Perl, I used the ternary operator to write it like this:
my $type = ($parameters{type} ($parameters{type} =~ /^(\w+)$/)) ? $1 :
'page';
While this is not the most beautiful code to look at, I have a weakness for
compact programs - so can I shorten the Python equivalent somehow?
Thanks,
Jan
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street. - Doug Linder
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[Tutor] Fetching dictionaries using MySQLdb
Hi, in Perl's DBI, I used fetchrow_hashref() to receive a database row as a dictionary, with the field names being the dictionary keys. MySQLdb's fetchone() returns a tuple Unfortunately, I have a dictionary of SQL queries which return rows of different lengths (read: with a varying number of fields). The documentation for MySQLdb says that fetchoneDict() is deprecated and the usage of fetchone() is suggested. Is there a recommended way to receive the results of an SQL query in the form I need? Or do I have to create a dictionary of fieldname tuples which can be zipped with the query result tuple? Thanks, Jan -- Any sufficiently advanced technology is indistinguishable from a Perl script. - Programming Perl ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Fetching dictionaries using MySQLdb
Kent Johnson wrote on 08.08.2005: Jan Eden wrote: The documentation for MySQLdb says that fetchoneDict() is deprecated and the usage of fetchone() is suggested. You could just use fetchoneDict(); deprecated isn't the same as gone... I tend to avoid deprecated functions/methods - I would need another method sooner or later anyway. Is there a recommended way to receive the results of an SQL query in the form I need? Or do I have to create a dictionary of fieldname tuples which can be zipped with the query result tuple? You can create a list of field names from the cursor.description attribute. But if the number of fields in the result varies how do you know which field goes with which description? That works, thank you. I will use the cursor.description attribute immediately after executing a query, so it will contain the correct field descriptions whenever I need them. The rest of my program uses the type attribute to decide which fields are present and which are not. All this is part of a port from Perl to Python - I will publish a log of everything I encountered in a couple of weeks. Cheers, Jan -- There's no place like ~/ ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Fetching dictionaries using MySQLdb
Hi Danny, Danny Yoo wrote on 08.08.2005: On Mon, 8 Aug 2005, Jan Eden wrote: Is there a recommended way to receive the results of an SQL query in the form I need? Or do I have to create a dictionary of fieldname tuples which can be zipped with the query result tuple? Hi Jan, MySQLdb supports the concept of customized cursor types. They have a particular cursor class that returns dictionary objects: Great! I found the pydoc for MySQLdb a bit confusing and would probably have taken quite a while to figure that out - thanks a lot. - Jan -- Any technology which is distinguishable from magic is insufficiently advanced. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Class instantiation parameters
Hi,
after using Perl for some years for simple scripting tasks, one of my programs
reached a size where an OO design is appropriate. So I rewrote the program
using OO techniques in Perl. Because I am not entirely satisfied with the
implementation, I decided port the program to Python.
The first thing I'd like to sort out are the parameters on class invocation. In
Perl, I did (... for lines left out):
my $page = Show-new(type = $type, id = $id);
package Show;
...
sub new {
my $class = shift;
my $self = { @_ };
...
bless $self, $class;
return $self;
}
making use of the relatively liquid border between hashes (dictionaries) and
arrays (lists).
In Python, I would do:
page = Show(type=type, id=id)
class Show:
def __init__(self, type, id):
self.id = id
self.type = type
...
return self
For two parameters, this is relatively simple. But if I have for example 10
parameters on instantiation, assigning each value the the class object manually
will be really clumsy.
So how can I add the values of all the paramaters to my class instance in one
step?
Thanks in advance,
Jan
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This happens to us all the time with computers, and nobody thinks of
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Re: [Tutor] Class instantiation parameters
Hi, Jan Eden wrote on 07.08.2005: So how can I add the values of all the paramaters to my class instance in one step? apologies for replying to my own post: I just discovered the **args formal parameter. Thanks, Jan -- I was gratified to be able to answer promptly, and I did. I said I didn't know. - Mark Twain ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Class instantiation parameters
Hi Kent,
Kent Johnson wrote on 07.08.2005:
So how can I add the values of all the paramaters to my class
instance in one step?
There was recently a long discussion of this on comp.lang.python.
http://groups.google.com/group/comp.lang.python/browse_frm/thread/
7346ad00a14e821a/9dc993d295475cac?q=locals()rnum=15hl=en#
9dc993d295475cac
Thanks for this. I thought I could do it with the help of **args, but maybe I
still think too much in Perl terms. It's a bit unexpected that this task asks
for such an indirect approach.
In Perl, where my class instances are usually nothing but (blessed) hash
references, a more verbose version of my actual method would read:
package NewClass;
...
sub new {
my $self = shift;
my $parameters = { @_ };
for (keys %$parameters) { $self-{$_} = $parameters-{$_};
}
My idea was to transfer the same technique to Python like this:
class NewClass:
def __init__(self, **parameters):
for i in parameters.keys(): self.i = parameters[i]
But the assignment in the for loop obviously does not work with instance
attributes. I will have to read up some more about instance attributes.
Thanks again,
Jan
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Re: [Tutor] Class instantiation parameters
Jan Eden wrote on 07.08.2005:
But the assignment in the for loop obviously does not work with
instance attributes. I will have to read up some more about instance
attributes.
Ok... so this works:
class NewClass:
def __init__(self, **parameters):
self.data = {}
for i in parameters.keys(): self.data[i] = parameters[i]
self = NewClass(arg1='Value', arg2='Another value', arg3='Yet another value')
print self.data
It seems that I need to add a dictionary as a data attribute to my instance
object to do what I wanted to.
This is unfortunate, because it complicates my syntax: Instead of self.type, I
need to use self.data['type'].
- Jan
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Marx
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Re: [Tutor] Class instantiation parameters
Hi Kent, hi Alan, Alan G wrote on 07.08.2005: page = Show(type=type, id=id) class Show: def __init__(self, type, id): self.id = id ... return self First a couple of comments. You don't need to return self from __init__. You can only instantiate Show *after* you've defined it. Right - I still think along the lines of Perl subroutines used as methods. **args is indeed the solution to this so you may have figured it all out already, but your terminology is slightly confusing (because while it is strictly valid in what it says, but so unlikely in its meaning, that I suspect you are getting some of your terms mixed up?) The idea is to pass keyword arguments to an instantiation function and automatically create instance attributes for each keyword argument. My apologies if I still mix up some well-defined terms in Python. Kent Johnson wrote on 07.08.2005: for i in parameters.keys(): setattr(self, i, parameters[i]) or for k, v in parameters.items(): setattr(self, k, v) The problem with this approach is that the function can be called with any number of arguments - you lose the limited type safety you get from declaring the arguments in the def - and it only works with keyword arguments, not positional arguments. Thanks! The setattr function is exactly what I was looking for. I should not need to worry about type safety, because the instance is instantiated from within a script after making sure that id is an integer and type is a string from a predefined set of strings. Now I'll see if I understand the practical difference between items() and iteritems() - the Python tutorial uses iteritems() in such a context. If you really just want a dictionary, maybe you should just use one? If you want the syntactic sugar of attribute access instead of dictionary lookup you could make a dict subclass that supports that. I do not really want a dictionary - I just want to pass some named parameters and turn them into attributes. But I will check out the recipes anyway. This is a really friendly and helpful list. Thanks again for all your help. - Jan -- Mac OS X. Because making Unix user-friendly is easier than debugging Windows. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
