Re: Logic operators with in statement
On Mon, Nov 16, 2009 at 6:02 AM, Mr.SpOOn mr.spoo...@gmail.com wrote:
Hi,
I'm trying to use logical operators (or, and) with the in statement,
but I'm having some problems to understand their behavior.
In [1]: l = ['3', 'no3', 'b3']
In [2]: '3' in l
Out[2]: True
In [3]: '3' and '4' in l
Out[3]: False
In [4]: '3' and 'no3' in l
Out[4]: True
This seems to work as I expected.
No, it doesn't. You are misinterpreting. Membership tests via `in` do
NOT distribute over `and` and `or`.
'3' and '4' in l
is equivalent to:
('3') and ('4' in l)
Recall that non-empty sequences and containers are conventionally True
in Python, so your expression is logically equivalent to:
'4' in l
With '3' not being checked for membership at all.
To check multiple items for membership in a contains, you must write
each `in` test separately and then conjoin then by the appropriate
boolean operator:
'3' in l and '4' in l
Cheers,
Chris
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Re: Logic operators with in statement
On Mon, Nov 16, 2009 at 6:08 AM, Mr.SpOOn mr.spoo...@gmail.com wrote:
Sorry for replying to myself, but I think I understood why I was wrong.
The correct statement should be something like this:
In [13]: ('b3' and '5') in l or ('3' and 'b3') in l
Out[13]: True
No, you've just run into another misunderstanding.
Given the expression `X and Y`:
If bool(X) is False, it evaluates to X.
Otherwise, it evaluates to Y.
In other words, the subexpression which ends up determining the truth
of the conjunction is what the conjunction evaluates to. `or` works
similarly.
This allows for tricky tricks like:
foo = possiblyFalse or default # use default if given value is false
Thus, due to the parentheses, your expression is equivalent to:
'5' in l or 'b3' in l
Which I trust is not what you intended.
Again, you need to write separate `in`s for each item you need to
check the membership of:
('b3' in l and '5' in l) or ('3' in l and 'b3' in l)
Cheers,
Chris
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Re: Logic operators with in statement
On Mon, Nov 16, 2009 at 6:23 AM, Xavier Ho cont...@xavierho.com wrote: snip '3' in l and 'no3' in l True AND operator has a higher precedence, so you don't need any brackets here, I think. But anyway, you have to use it like that. So that's something you'll have to fix first. Er, you mean lower precedence. Higher precedence means it would bind tighter, thus the expression would mean: '3' in (l and 'no3') in l which is certainly incorrect. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Language mavens: Is there a programming with if then else ENDIF syntax?
On Mon, Nov 16, 2009 at 8:54 AM, Steve Ferg
steve.ferg.bitbuc...@gmail.com wrote:
This is a question for the language mavens that I know hang out here.
It is not Python related, except that recent comparisons of Python to
Google's new Go language brought it to mind.
NOTE that this is *not* a suggestion to change Python. I like Python
just the way it is. I'm just curious about language design.
For a long time I've wondered why languages still use blocks
(delimited by do/end, begin/end, { } , etc.) in ifThenElse statements.
I've often thought that a language with this kind of block-free syntax
would be nice and intuitive:
if condition then
do stuff
elif condition then
do stuff
else
do stuff
endif
Note that you do not need block delimiters.
snip
Does anybody know a language with this kind of syntax for
ifThenElseEndif?
Ruby:
if count 10
puts Try again
elsif tries == 3
puts You lose
else
puts Enter a number
end
Cheers,
Chris
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Re: Web servers
On Mon, Nov 16, 2009 at 11:17 AM, Virgil Stokes v...@it.uu.se wrote: Any suggestions on using Python to connect to Web servers (e.g. to access financial time series data)? In what format? Using what protocol? (*Insert other basic questions that need answering in order to answer your question here*) Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Changing the current directory (full post)
On Mon, Nov 16, 2009 at 11:36 AM, vsoler vicente.so...@gmail.com wrote: On Nov 16, 2:35 am, Gabriel Genellina gagsl-...@yahoo.com.ar wrote: En Sun, 15 Nov 2009 09:04:06 -0300, vsoler vicente.so...@gmail.com escribió: Ever since I installed my Python 2.6 interpreter (I use IDLE), I've been saving my *.py files in the C:\Program Files\Python26 directory, which is the default directory for such files in my system. However, I have realised that the above is not the best practice. Therefore I created the C:\Program Files\Python26\test directory and I want it to be my default directory for saving *.py files, importing modules, etc. This is *not* a good place either. Non-privileged users should not have write permission in the C:\Program Files directory. I'd like to do something like the DOS equivalent of CD test but I do not know kow to do it. I am currently doing something really awful: I open a *.py file in the test subdirectory, I run it with the F5 key and it works! but I am doing really something stupid. it works! What's the problem then? How should I proceed, if I want to proceed properly? Sorry but I don't even see your problem. You can save your .py files anywhere you like... -- Gabriel Genellina Gabriel, When I enter IDLE, I'd like to say at the prompt: my current directory is... ...test and then be able to run a module in that directory. This is what my problem is!!! 1. File - Open 2. Navigate to file and choose it 3. Press F5 Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Changing the current directory (full post)
On Mon, Nov 16, 2009 at 11:56 AM, vsoler vicente.so...@gmail.com wrote: On Nov 16, 8:45 pm, Chris Rebert c...@rebertia.com wrote: On Mon, Nov 16, 2009 at 11:36 AM, vsoler vicente.so...@gmail.com wrote: On Nov 16, 2:35 am, Gabriel Genellina gagsl-...@yahoo.com.ar wrote: En Sun, 15 Nov 2009 09:04:06 -0300, vsoler vicente.so...@gmail.com escribió: Ever since I installed my Python 2.6 interpreter (I use IDLE), I've been saving my *.py files in the C:\Program Files\Python26 directory, which is the default directory for such files in my system. However, I have realised that the above is not the best practice. Therefore I created the C:\Program Files\Python26\test directory and I want it to be my default directory for saving *.py files, importing modules, etc. This is *not* a good place either. Non-privileged users should not have write permission in the C:\Program Files directory. I'd like to do something like the DOS equivalent of CD test but I do not know kow to do it. I am currently doing something really awful: I open a *.py file in the test subdirectory, I run it with the F5 key and it works! but I am doing really something stupid. it works! What's the problem then? How should I proceed, if I want to proceed properly? Sorry but I don't even see your problem. You can save your .py files anywhere you like... When I enter IDLE, I'd like to say at the prompt: my current directory is... ...test and then be able to run a module in that directory. This is what my problem is!!! 1. File - Open 2. Navigate to file and choose it 3. Press F5 Say that you wanted to import a file in the test directory after just entering IDLE. How would you do it? import sys sys.path.insert(0, C:/path/to/test/dir/here) import something_in_test_dir Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: faster than list.extend()
On Mon, Nov 16, 2009 at 2:30 PM, Hyunchul Kim hyunchul.mail...@gmail.com wrote: Hi, all. I want to improve speed of following simple function. Any suggestion? ** def triple(inputlist): results = [] for x in inputlist: results.extend([x,x,x]) return results ** You'd probably be better off calling .append() 3 times instead of .extend() as it would avoid the creation of all those intermediate 3-element lists. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Get attribute this way
On Mon, Nov 16, 2009 at 10:04 PM, King animator...@gmail.com wrote: Python's getattr, setattr and __getattribute__ commands works fine with python types. For example: print o.__getattribute__(name) print getattr(o, name) This is the easiest way to get an attribute using a string. In my case the Node class load/creates all the attributes from a xml file. Example Input name=position type=float value=0.5/ Input name=color type=color value=0,0,0/ There are certain atrributes of compound type. Example: # Array of colors, Here we are referring first color and second element (green) self.gradient.colors[0][1] = 0.5 # Array of floats, referring first element self.gradient.positions[0] = 1.0 Color, color array and floats are all custom classes. Now question is how to get these compound attributes using string as we do with default singular attributes. Example: getattr(o, gradient.colors[0][1] ) I need this to save the data of nodes-attributes into a custom xml format, when loading this data back, I create the node first and then setup values from the saved xml file. Can't you just iterate over the data structure? I'm not seeing why you'd need to use getattr() and friends in the first place. for color in self.gradient.colors: for element in color: #output XML fragment #repeat for self.gradient.positions, etc. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Get attribute this way
On Mon, Nov 16, 2009 at 10:53 PM, King animator...@gmail.com wrote: Writing/Reading data to xml is not a problem. The problem is when I have to write to attributes in xml, where a connections has been established. XML: Connection sourceattribute=node1.gradient.colors[0][1] destattribute=node2.gradient.colors[1][2]/ You did not include an example like this in your original post. I'd say you're stuck using eval() unless you want to change your format or write a parser for the subset of Python involved. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Accessing a Web server --- how?
On Mon, Nov 16, 2009 at 2:14 AM, Virgil Stokes v...@it.uu.se wrote: If one goes to the following URL: http://www.nordea.se/Privat/Spara%2boch%2bplacera/Strukturerade%2bprodukter/Aktieobligation%2bNr%2b99%2bEuropa%2bAlfa/973822.html it contains a link (click on Current courses NBD AT99 3113A) to: http://service.nordea.com/nordea-openpages/six.action?target=/nordea.public/bond/nordeabond.pagemagic=%28cc+%28detail+%28tsid+310746%29%29%29; and if you now click on the tab labeled history and compare this will take you to: http://service.nordea.com/nordea-openpages/six.action?target=/nordea.public/bond/nordeabond.pagemagic=%28cc+%28detail+%28tsid+310746%29+%28view+hist%29%29%29; Finally...This is where I would like to connect to the data on a daily basis or to gather data over different time intervals. I believe that if I can get some help on this, then I will be able to customize the code as needed for my own purposes. HTML parsing: http://www.crummy.com/software/BeautifulSoup/ Downloading webpages: http://docs.python.org/library/urllib.html#urllib.urlopen BeautifulSoup is excellently documented: http://www.crummy.com/software/BeautifulSoup/documentation.html You'll probably be interested in the sections on searching and navigating the parse tree. Cheers, Chris -- IANAL and do not condone violating website TOSes http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: TODO and FIXME tags
2009/11/16 Yasser Almeida Hernández pedro...@fenhi.uh.cu: Hi all.. Sorry if this question sound elemental. How is the sintaxis for set the TODO and FIXME tags...? There is no special syntax for those. Some people use them in comments, but it's just a convention. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Code for finding the 1000th prime
On Tue, Nov 17, 2009 at 9:27 AM, Diez B. Roggisch de...@nospam.web.de wrote: Stefan Behnel wrote: Robert P. J. Day, 15.11.2009 15:44: Now, all that's left to do is write a prime number generator (a random number generator will do, too, but writing a good one isn't easy), run it repeatedly in a loop, and check if the returned number is 7919. Once it compares equal, you can print the result and you're done. That reminds me of the only algorithm I really invented myself: debil sort. There's prior art for this algorithm: http://en.wikipedia.org/wiki/Bogosort It goes like this: L = list of comparable items while not sorted(L): p = generate_random_permutation(len(L)) L = apply_permutation(L, p) print L Great algorithm. Actually works. And the saddest thing: somebody out there certainly has written something like that by accident... I've spotted sorting in O(n^3) (with non-deterministic exceptional termination conditions) already in the wild. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: python simply not scaleable enough for google?
On Tue, Nov 17, 2009 at 8:41 AM, Rustom Mody rustompm...@gmail.com wrote: Language L is (in)efficient. No! Only implementations are (in)efficient I am reminded of a personal anecdote. It happened about 20 years ago but is still fresh and this thread reminds me of it. I was attending some workshop on theoretical computer science. I gave a talk on Haskell. I showed off all the good-stuff -- pattern matching, lazy lists, infinite data structures, etc etc. Somebody asked me: Isnt all this very inefficient? Now at that time I was a strong adherent of the Dijkstra-religion and this viewpoint efficiency has nothing to do with languages, only implementations traces to him. So I quoted that. Slowing the venerable P S Thiagarajan got up and asked me: Lets say that I have a language with a type 'Proposition' And I have an operation on proposition called sat [ sat(p) returns true if p is satisfiable]... I wont complete the tale other than to say that Ive never had the wind in my sails taken out so completely! So Vincent? I wonder what you would have said in my place? I'm not Vincent, but: The sat() operation is by definition in inefficient, regardless of language? Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: TypeError: unsupported operand types for +: 'NoneType' and 'str'
On Tue, Nov 17, 2009 at 7:25 PM, aurfal...@gmail.com wrote:
snip
The error I get;
File myscript.py, Line 18, in ?
projectpath = ourHome+/etc/TEMPLATE
TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'
Python 2.4.3
I've read were when passing a string to exec may need to end with a '\n'
I've tried a few diff variations on the below line 18 w/o luck. Any one
mind helping out a bratha from anatha ... planet that is?
line 18;
projectpath = ourHome+/etc/TEMPLATE
line 17;
ourHome = os.environ.get('some_env')
From the `os` docs:
os.environ
A mapping object representing the string environment.
From the `dict` docs (`dict` being the built-in and prototypical mapping class):
D.get(k[,d]) - D[k] if k in D, else d. d defaults to None.
From this, I conclude that the environment variable `some_env` does
not exist for you, thus .get() returns None, thus causing an error
when you try and concatenate it with a string.
Solution: Either fix things so the environment variable does exist or
add code to handle the case of the environment variable not existing.
Cheers,
Chris
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Re: WindowsError is not available on linux?
On Tue, Nov 17, 2009 at 7:37 PM, Peng Yu pengyu...@gmail.com wrote: On Tue, Nov 17, 2009 at 9:18 PM, alex23 wuwe...@gmail.com wrote: Peng Yu pengyu...@gmail.com wrote: But the document doesn't say shutil need to be imported in order to use WindowsError. Shall the document or the code be corrected? Neither, it's your understanding that needs correction. Benjamin wasn't trying to say that WindowsError is defined within shutil, he was showing that it _isn't_ defined within shutil on a non- Windows machine. As you're looking in shutil.py, you should have noticed this at the very top, just beneath the declaration of the Error exception: try: WindowsError except NameError: WindowsError = None This looks for the existence of the WindowsError exception - present only under Windows - and if it's not there it binds the name to None. You'll notice that the only place it's used in shutil.py is prefixed by the test WindowsError is not None... I think the mention of the exception being raised when a Windows- specific error occurs should make it pretty clear that this is a Windows-only exception. I don't know about others. The wording Windows-specific error occurs was ambiguous to me. It could refers to some errors resulted from copying (on a linux machine) some files from linux file systems to windows files systems (via samba, maybe). I recommend to revise the document a little bit to avoid confusion. But your example isn't even Windows-specific because Samba server exists; any error would network-related or specific to the SMB protocol rather than Windows-related. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Running a python script from interactive mode
On Tue, Nov 17, 2009 at 8:56 PM, ashwini yal ashwini...@gmail.com wrote: Hi, I am trying to run a python script from interactive mode ,but i am not able to know how to run it? Is it possible? if yes please let me how to run the script? execfile(/path/to/the/script.py) or if it's on your sys.path and doesn't use the `if __name__ == __main__:` idiom then just importing it works: import script_name Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Language mavens: Is there a programming with if then else ENDIF syntax?
On Wed, Nov 18, 2009 at 1:15 AM, Steve Howell showel...@yahoo.com wrote:
On the topic of switch statements and even-more-concise-then-we-have-
already if/elif/else/end constructs, I have to say that Python does
occasionally force you to write code like the code below. Maybe
force is too strong a word, but Python lends itself to if/elif
blocks like below, which get the job done just fine, but which are not
syntactically pretty, due to the (el){0,1}if kind == duplication.
There are often cases where if/elif statements are just a smell that
you do not know how to do dictionary lookups, but if you converted the
below code to use dictionary lookups, you would complicate the code
almost as much as you abstracted the code, if not more, unless I am
just being very naive.
I'm gonna have to disagree and say using the dictionary dispatch
technique would clean it up a good bit.
Yes, it would entail creating several functions, but those functions
could then be documented (vs. the currently opaque code blocks); and
due to their separation and smaller length, they would be easier to
understand and test than the given code.
Additionally, the sheer length of the given code segment probably
constitutes a code smell in and of itself for the function containing
that code.
Cheers,
Chris
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Re: break LABEL vs. exceptions + PROPOSAL
On Wed, Nov 18, 2009 at 4:05 AM, Lo'oris loo...@gmail.com wrote: I've found this email, back from 10 years ago: http://mail.python.org/pipermail/python-list/1999-September/009983.html I guess it went unnoticed, because that proposal looks really intresting. • break labels have been refused into python • we can do it anyway using exceptions • this is a proposal for something better, resembling the exception way and much more powerful and python-like than break labels You're gonna have to wait 18-24 months: http://www.python.org/dev/peps/pep-3003/ Also, the python-ideas list might be a better forum for discussing this than the general-interest list: http://mail.python.org/mailman/listinfo/python-ideas Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Minimally intrusive XML editing using Python
On Wed, Nov 18, 2009 at 4:55 AM, Thomas Lotze tho...@thomas-lotze.de wrote: I wonder what Python XML library is best for writing a program that makes small modifications to an XML file in a minimally intrusive way. By that I mean that information the program doesn't recognize is kept, as are comments and whitespace, the order of attributes and even whitespace around attributes. In short, I want to be able to change an XML file while producing minimal textual diffs. Most libraries don't allow controlling the order of and the whitespace around attributes, so what's generally left to do is store snippets of original text along with the model objects and re-use that for writing the edited XML if the model wasn't modified by the program. Does a library exist that helps with this? Does any XML library at all allow structured access to the text representation of a tag with its attributes? Have you considered using an XML-specific diff tool such as: * One off this list: http://www.manageability.org/blog/stuff/open-source-xml-diff-in-java * xmldiff (it's in Python even): http://www.logilab.org/859 * diffxml: http://diffxml.sourceforge.net/ [Note: I haven't actually used any of these.] Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: DOM related question and problem
On Wed, Nov 18, 2009 at 10:04 AM, elca high...@gmail.com wrote:
Hello,
these day im making python script related with DOM.
problem is these day many website structure is very complicate .
what is best method to check DOM structure and path..
i mean...following is some example.
what is best method to check can extract such like following info quickly?
before i was spent much time to extract such info .
and yes im also new to python and DOM.
IE.Document.Frames(1).Document.forms('comment').value = 'hello'
if i use DOM inspector, can i extract such info quickly ? if so would you
show me some sample?
here is some site . i want to extract some dom info.
today i was spent all day long to extract what is dom info. but failed
http://www.segye.com/Articles/News/Politics/Article.asp?aid=20091118001261ctg1=06ctg2=00subctg1=06subctg2=00cid=010101060
at the end of this page,can find some comment input box.
i want to know what kind of dom element should have to use, such like
IE.Document.Frames(1).Document.forms('comment').value = 'hello'
anyhelp much appreciate thanks
This sounds suspiciously like a spambot. Why do you want to submit
comments in an automated fashion exactly?
Cheers,
Chris
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Re: DeprecationWarning on md5
On Wed, Nov 18, 2009 at 5:23 PM, Zeynel azeyn...@gmail.com wrote: Hello, I am a newbie both in Scrapy and Python. When I create a project with Scrapy I get these errors: C:\Python26\lib\site-packages\twisted\python\filepath.py:12: DeprecationWarning: the sha module is deprecated; use the hashlib module instead import sha C:\Python26\lib\site-packages\twisted\spread\pb.py:30: DeprecationWarning: the md5 module is deprecated; use hashlib instead import md5 C:\Python26\lib\site-packages\twisted\mail\smtp.py:10: DeprecationWarning: the MimeWriter module is deprecated; use the email package instead I found several references to this bug but I could not understand how to fix it. Can anyone help? This is a bug in the version of Twisted you're using. What Python is saying is that Twisted is using some modules from the Python stdlib that are deprecated and will be removed in some future version of Python, thus Twisted will /eventually/ need to be changed to use the newer replacement library. However, this is only a warning, not an error; the code will run just fine until you update to the eventual Python version that removed said deprecated libraries (by which time a new Twisted version will probably be available with the necessary fixes made). So, basically you can safely ignore the warnings, unless you want to custom-patch your Twisted installation, which I wouldn't particularly recommend. It's also entirely possible your Twisted is outdated and a new version fixed to avoid using the deprecated modules is already available. If you want to suppress the output of the warnings, see the docs for the `warnings` module: http://docs.python.org/library/warnings.html Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: combinatorics via __future__ generators
On Wed, Nov 18, 2009 at 4:58 PM, Phlip phlip2...@gmail.com wrote: Python: I have a quaint combinatorics problem. Before I solve it, or find a solution among generators, I thought y'all might like to show off any solutions. Given an array like this... [0, 4, 3] Produce an array like this: [ [0, 0, 0], [0, 1, 0], [0, 2, 0], [0, 3, 0], [0, 1, 1], [0, 2, 1], [0, 3, 1], [0, 1, 2], [0, 2, 2], [0, 3, 2], ] The first array is the counts of options in 4 slots, and the second is all combinations of indexes of each option, such that every option associates once with every other option. The leading 0 simply represents a slot with no options; the algorithm must preserve those. This should be child's play for the generator package, right? from itertools import imap, product def special_range(n): return (xrange(n) if n else [0]) def something(arr): return product(*imap(special_range, arr)) print list(something([0,4,3])) Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: What is the naming convention for accessor of a 'private' variable?
On Wed, Nov 18, 2009 at 6:27 PM, Peng Yu pengyu...@gmail.com wrote: http://www.python.org/dev/peps/pep-0008/ The above webpage states the following naming convention. Such a variable can be an internal variable in a class. I'm wondering what is the naming convention for the method that access such variable. - _single_leading_underscore: weak internal use indicator. E.g. from M import * does not import objects whose name starts with an underscore. If there's a method to access the variable, then it's not all that private, is it? Accessor methods are not Pythonic. Just make the attribute public by not prefixing it with an underscore. See also Python is Not Java: http://dirtsimple.org/2004/12/python-is-not-java.html Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Invitation to connect on LinkedIn
On Wed, Nov 18, 2009 at 6:16 PM, Jim Qiu bluefishe...@gmail.com wrote: LinkedIn Jim Qiu requested to add you as a connection on LinkedIn: Jaime, I'd like to add you to my professional network on LinkedIn. - Jim Accept View invitation from Jim Qiu WHY MIGHT CONNECTING WITH JIM QIU BE A GOOD IDEA? Jim Qiu's connections could be useful to you After accepting Jim Qiu's invitation, check Jim Qiu's connections to see who else you may know and who you might want an introduction to. Building these connections can create opportunities in the future. © 2009, LinkedIn Corporation -- http://mail.python.org/mailman/listinfo/python-list Could one of the list admins please reset the password and change the email on this guy's LinkedIn account? How the heck someone sets their account email to a mailinglist, I'll never figure out. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: convert a string to a regex?
On Wed, Nov 18, 2009 at 6:51 PM, Peng Yu pengyu...@gmail.com wrote: There are many special characters listed on http://docs.python.org/library/re.html I'm wondering if there is a convenient function that can readily convert a string with the special characters to its corresponding regex. For example, some.thing = some\.thing If you'd taken 45 seconds to scan the documentation: http://docs.python.org/library/re.html#re.escape re.escape(string) Return string with all non-alphanumerics backslashed; this is useful if you want to match an arbitrary literal string that may have regular expression metacharacters in it. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: What is the naming convention for accessor of a 'private' variable?
On Wed, Nov 18, 2009 at 7:04 PM, Peng Yu pengyu...@gmail.com wrote: On Wed, Nov 18, 2009 at 8:47 PM, Chris Rebert c...@rebertia.com wrote: On Wed, Nov 18, 2009 at 6:27 PM, Peng Yu pengyu...@gmail.com wrote: http://www.python.org/dev/peps/pep-0008/ The above webpage states the following naming convention. Such a variable can be an internal variable in a class. I'm wondering what is the naming convention for the method that access such variable. - _single_leading_underscore: weak internal use indicator. E.g. from M import * does not import objects whose name starts with an underscore. If there's a method to access the variable, then it's not all that private, is it? Accessor methods are not Pythonic. Just make the attribute public by not prefixing it with an underscore. See also Python is Not Java: http://dirtsimple.org/2004/12/python-is-not-java.html I don't quite understand the following paragraph from the above webpage. Would you please give me an example to help me understand it? Here's what you do. You write a function that contains a function. The inner function is a template for the functions that you're writing over and over again, but with variables in it for all the things that vary from one case of the function to the next. The outer function takes parameters that have the same names as those variables, and returns the inner function. Then, every place where you'd otherwise be writing yet another function, simply call the outer function, and assign the return value to the name you want the duplicated function to appear. Now, if you need to change how the pattern works, you only have to change it in one place: the template. #untested off-the-cuff example: from time import time def add_timing(func): # takes a function as an argument Wraps functions so they output their execution time when called def wrapper(*args, **kwargs): #defines a new function start = time() # thanks to closures, we can access func here result = func(*args, **kwargs) # have the new function call the given function end = time() duration = end-start print Call to, func.__name__, took, duration, seconds return result return wrapper # return the new function so that it can replace the function it calls def long_calculation(x, y, z): # some code long_calculation = add_timing(long_calculation) print long_calculation(1, 7, 42) #Example output: #Call to long_calculation took 135.5 seconds #99 Now imaging applying add_timing to multiple functions and note the amount of code you'd save and how the unrelated concerns of timing and mathematical calculation (or whatever the functions you apply add_timing() to do) would then be cleanly separated. The same technique can be applied to logging and other repetitive code to factor it out. It's sort of like aspect-oriented programming, but not as kludgey. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: crontab problem
On Sat, Nov 21, 2009 at 5:47 AM, Victor Subervi victorsube...@gmail.com wrote: Hi; I have the following in crontab -eu root: @daily /usr/local/bin/mysql-backup-daily.sh @weekly /usr/local/bin/mysql-backup-weekly.sh @monthly /usr/local/bin/mysql-backup-monthly.sh [r...@13gems globalsolutionsgroup.vi]# ls /usr/local/bin/mysql-* /usr/local/bin/mysql-daily.sh /usr/local/bin/mysql-monthly.sh /usr/local/bin/mysql-weekly.sh These scripts worked on another server. The daily writes to: /usr/backup/database/mysql-backups/mysql-backup-dailys/ However, a day later, nothing is there. Please advise. And this is germane to Python (and not instead say, *nix) how exactly? Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Sorting: too different times. Why?
On Sun, Nov 22, 2009 at 2:56 AM, n00m n...@narod.ru wrote: I was expecting the 1st method would be *slower* than the 2nd one :-) Or at least equal... Just random (intuitive) expectations The second method repeatedly looks up left_item.__class__.__cmp__ (i.e. Vector.__cmp__) when doing the necessary comparisons between the list items; while these lookups are optimized and are fast, they are not free and cannot be skipped because Python doesn't know the list contains only Vectors. The first method uses the single provided comparison function and thus does no such lookups; hence, it's faster. That's my guess anyway. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Why Python allows comparison of a callable and a number?
On Sun, Nov 22, 2009 at 4:03 AM, 一首诗 newpt...@gmail.com wrote: I used python to write an assignment last week, here is a code snippet # def departTime(): ''' Calculate the time to depart a packet. ''' if(random.random 0.8): t = random.expovariate(1.0 / 2.5) else: t = random.expovariate(1.0 / 10.5) return t # Can you see the problem? I compare random.random with 0.8, which should be random.random(). Of course this because of my careless, but I don't get it. In my opinion, this kind of comparison should invoke a least a warning in any programming language. So why does python just ignore it? It's an historical anomaly that's been rectified in Python 3, where such non-equality comparisons between unrelated types *do* now raise an error. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: attributes, properties, and accessors -- philosophy
On Mon, Nov 23, 2009 at 10:52 AM, Ethan Furman et...@stoneleaf.us wrote: The problem I have with properties is my typing. I'll end up assigning to an attribute, but get the spelling slightly wrong (capitalized, or missing an underscore -- non-obvious things when bug-hunting), so now I have an extra attribute which of course has zero effect on what I'm trying to do and I start getting wierd results like viewing deleted records when I *know* I set useDeleted = False... 30 minutes later I notice it was /supposed/ to be use_deleted. *sigh* So -- to keep myself out of trouble -- I have started coding such things as, for example: result = table.use_deleted() # returns True or False table.use_deleted(False) # skip deleted records instead of result = table.use_deleted table.use_deleted = False My question: is this [ severely | mildly | not at all ] un-pythonic? Yes, it's unpythonic. Use something like pychecker, pylint, or pyflakes, which will catch the sorts of typo errors you talk about. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: pointless musings on performance
On Tue, Nov 24, 2009 at 4:31 AM, Rob Williscroft r...@freenet.co.uk wrote: mk wrote in news:mailman.915.1259064240.2873.python-l...@python.org in comp.lang.python: def pythonic(): def unpythonic(): Decidedly counterintuitive: are there special optimizations for if nonevar: type of statements in cpython implementation? from dis import dis dis( unpythonic ) 18 31 LOAD_FAST 0 (nonevar) 34 LOAD_CONST 0 (None) 37 COMPARE_OP 9 (is not) 40 JUMP_IF_FALSE 4 (to 47) dis( pythonic ) 11 31 LOAD_FAST 0 (nonevar) 34 JUMP_IF_FALSE 4 (to 41) In other words, CPython doesn't happen to optimize `if nonevar is not None` as much as it theoretically could (which would essentially require a JUMP_IF_NONE opcode). Since CPython isn't known for doing fancy optimizations, this isn't surprising. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: attributes, properties, and accessors -- philosophy
On Tue, Nov 24, 2009 at 9:39 AM, Ethan Furman et...@stoneleaf.us wrote: Bruno Desthuilliers wrote: Ethan Furman a écrit : The problem I have with properties is my typing. I'll end up assigning to an attribute, but get the spelling slightly wrong (capitalized, or missing an underscore -- non-obvious things when bug-hunting), so now I have an extra attribute which of course has zero effect on what I'm trying to do and I start getting wierd results like viewing deleted records when I *know* I set useDeleted = False... 30 minutes later I notice it was /supposed/ to be use_deleted. *sigh* So -- to keep myself out of trouble -- I have started coding such things as, for example: result = table.use_deleted() # returns True or False table.use_deleted(False) # skip deleted records instead of result = table.use_deleted table.use_deleted = False My question: is this [ severely | mildly | not at all ] un-pythonic? Definitly and totally unpythonic. The first solution to your problem is to stick to standard naming conventions. If this is not enough, Chris pointed you to really useful tools. Also, you can override __setattr__ to catch such errors - at least during the coding/debug phase. Good tools to know about, and a consistent naming pattern also makes life easier (which I have since done ;). Let's head towards murkier waters (at least murkier to me -- hopefully they can be easily clarified): some of the attributes are read-only, such as record count; others are not directly exposed, but still settable, such as table version; and still others require a small amount of processing... at which point do I switch from simple attribute access to method access? Thanks to the magic of properties, the end-user-programmer need not know which you're using: http://docs.python.org/library/functions.html#property Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: get line number and filename in a source file
On Tue, Nov 24, 2009 at 9:47 PM, Peng Yu pengyu...@gmail.com wrote: __LINE__ __FILE__ in C++ can give the current line number and filename. Is there a similar thing in python that can give me the current line number and filename? import inspect filename, linenum, funcname = inspect.getframeinfo(inspect.currentframe())[:3] Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Can self crush itself?
On Wed, Nov 25, 2009 at 1:46 AM, n00m n...@narod.ru wrote: Then how can we destroy the 3rd instance, right after its creation and from inside class Moo code? Why would you want to do that in the first place? It's strange to say the least. If you want to prevent an instance being created in the first place, you can override __new__(). Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Feature request: String-inferred names
On Wed, Nov 25, 2009 at 6:35 PM, The Music Guy fearsomedragon...@gmail.com wrote: Hello all, I just posted to my blog about a feature that I'd like to see added to Python. Before I go through the trouble of learning how to write a PEP or how to extend the Python interpreter, I want to know what people in the community have to say about it. http://alphaios.blogspot.com/2009/11/python-string-inferred-names-working.html As far as I know, a feature like this does not appear in any existing PEPs. (If it does I would appreciate it if someone could tell me what PEP it is.) Please give and comments you may have, but I request that you be constructive if you must criticize...thank you! Ugly, Perlish, and as you even admit, entirely unnecessary. And you'd need to wait at least a year anyway: http://www.python.org/dev/peps/pep-3003/ Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: semantics of ** (unexpected/inconsistent?)
On Sun, Nov 29, 2009 at 4:39 PM, Esmail ebo...@hotmail.com wrote: Ok, this is somewhat unexpected: Python 2.6.2 (release26-maint, Apr 19 2009, 01:56:41) [GCC 4.3.3] on linux2 Type help, copyright, credits or license for more information. -3**2 -9 x = -3 x**2 9 I would have expected the same result in both cases. Initially I would have expected -3**2 to yield 9, but I can accept that ** binds tighter than the unary -, but shouldn't the results be consistent regardless if I use a literal or a variable? _No_, because using the variable evaluates -3 as a unit separately by itself, before the exponentiation ever occurs; it's the same as the difference between (-3)**2 and -3**2. Python is not a concatenative programming language[*]; you can't directly textually replace a variable with its value and expect to get the same result from an expression. For instance, in this case, you need to add the parentheses. Cheers, Chris -- http://blog.rebertia.com [*] http://en.wikipedia.org/wiki/Concatenative_language -- http://mail.python.org/mailman/listinfo/python-list
Re: Noobie python shell question
On Sun, Nov 29, 2009 at 7:53 PM, Tim Chase python.l...@tim.thechases.com wrote: snip (as an aside, is there a way to get a local/global variable from a string like one can fetch a variable from a class/object with getattr()? Something like getattr(magic_namespace_here, hello) used in the above context? I know it can be done with eval(), but that's generally considered unsafe unless you vet your input thoroughly) locals()[hello] and globals()[hello], respectively Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Unpacking Tuples
On Mon, Nov 30, 2009 at 12:17 AM, Joel Davis callmeclaud...@gmail.com wrote: I hate to post such a simple Q and A here, but I seriously can't find it anywhere. Python (unsure of starting with which version) enables the remainder of the tuple to be placed in a catch-all, for example: myTuple = (1,2,3,4) varOne, varTwo, *remaindingTuple = myTuple. where the values left unpacked get thrown into a tuple referenced to by remaindingTuple I included the asterix because it seems like I remember that being the operator that specifying the tuple's dumping ground. Which brings me to my two questions: 1) what's the syntax for this operation Exactly as you showed above (well, minus the period obviously). 2) what version does it start with? Python 3.0 It might be backported into 2.7 when it gets released: http://bugs.python.org/issue2340 Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: python and vc numbers
On Mon, Nov 30, 2009 at 2:02 AM, Daniel Dalton d.dal...@iinet.net.au wrote: On Mon, Nov 30, 2009 at 07:20:59PM +1100, Daniel Dalton wrote: That did the trick, thanks, after I append [-2] Further testing under screen says otherwise -- it seems to give me the tty number, not the virtual console number. Is there any way to figure out what virtual console I'm am in so a certain command ran under screen process A isn't confused with a command ran under screen process B? From what I can find, virtual console == tty. Quoting http://en.wikipedia.org/wiki/Virtual_console_%28PC%29 The virtual consoles are represented by device special files /dev/tty1, /dev/tty2 etc. Also, in my quickie newbie experimentation with `screen`, each screen window seems to get a unique tty#. Admittedly I am running OS X here, so if your notion of virtual console differs from Wikipedia's and is Linux-specific or something... Perhaps if you could explain your problem in greater detail? Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: semantics of ** (unexpected/inconsistent?)
On Mon, Nov 30, 2009 at 3:46 AM, Gregory Ewing greg.ew...@canterbury.ac.nz wrote: Esmail wrote: Wow .. never heard of Concatenative_languages languages before or the distinction you make. Your distinction explains the behavior, but I find it somewhat counter-intuitive. You shouldn't find it any more surprising than the fact that a = 2 + 3 print a * 5 gives a different result from print 2 + 3 * 5 On Mon, Nov 30, 2009 at 3:41 AM, inhahe inh...@gmail.com wrote: one point of confusion could be the use of ** instead of superscript. it might make things a little bit more counterintuitive-looking than with superscripts, since the issue with Well, since source code is almost universally just plain ASCII and not in some file format with typesetting, superscripts aren't going to happen any time soon. (Also, avoid top-posting in the future.) Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Function parameters list
On Tue, Dec 1, 2009 at 12:15 AM, Nadav Chernin nada...@qualisystems.com wrote: Hello, all I need to know dynamically parameters of any function (prototype). Is there some way to get it? The `inspect` module: http://docs.python.org/library/inspect.html#inspect.getargspec http://docs.python.org/library/inspect.html#inspect.formatargspec Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: python bijection
On Tue, Dec 1, 2009 at 5:17 PM, Aahz a...@pythoncraft.com wrote: In article 85100df7-a8b0-47e9-a854-ba8a8a2f3...@r31g2000vbi.googlegroups.com, Joshua Bronson jabron...@gmail.com wrote: I noticed the phonebook example in your ActiveState recipe and thought you might consider changing it to something like husbands to wives, since the names-to-phone-numbers relation is many-to-many. What makes you think husbands to wives is one-to-one? ;-) (Even assuming monogamy, you have husbands-to-husbands and wives-to-wives.) Reminds me of this quite funny blog post: Gay marriage: the database engineering perspective http://qntm.org/?gay Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: commands module for windows
On Tue, Dec 1, 2009 at 10:05 PM, M Kumar tomanis...@gmail.com wrote: Is there any python module for windows which is equivalent to commands module in linux? `subprocess` should work: http://docs.python.org/library/subprocess.html The `commands` docs even say: The subprocess module provides more powerful facilities for spawning new processes and retrieving their results. Using the subprocess module is preferable to using the commands module. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: commands module for windows
On Wed, Dec 2, 2009 at 11:42 AM, Chris Rebert c...@rebertia.com wrote: On Tue, Dec 1, 2009 at 10:05 PM, M Kumar tomanis...@gmail.com wrote: Is there any python module for windows which is equivalent to commands module in linux? `subprocess` should work: http://docs.python.org/library/subprocess.html The `commands` docs even say: The subprocess module provides more powerful facilities for spawning new processes and retrieving their results. Using the subprocess module is preferable to using the commands module. On Tue, Dec 1, 2009 at 10:34 PM, M Kumar tomanis...@gmail.com wrote: can I use this module to store output to a python variable? I am looking for something similar to commands.getoutput(cmd) Yes, of course it can. If it's more powerful, then it can do everything the other module can. It'd be silly for the `commands` docs to point people to `subprocess` if this wasn't the case. It will take more than a single line of code though. Read the module's docs. Regards, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Don't Understand This Error
On Wed, Dec 2, 2009 at 2:33 AM, Victor Subervi victorsube...@gmail.com wrote:
I get the following error:
/var/www/html/angrynates.com/cart/chooseOptions.py
8 from login import login
9 import string
10 import options
11 from particulars import optionsTables, addStore
12
options undefined
SyntaxError: invalid syntax (options.py, line 140)
args = ('invalid syntax',
('/var/www/html/angrynates.com/cart/options.py', 140, 85, colorsTables,
colorsNames = colors('products', 'specificTables', specificTables):\n))
filename = '/var/www/html/angrynates.com/cart/options.py'
lineno = 140
msg = 'invalid syntax'
offset = 85
print_file_and_line = None
text = colorsTables, colorsNames = colors('products',
'specificTables', specificTables):\n
I don't understand the 'text = ... part of the last line.
It's the text of the specific line of code that caused the error, I think.
Here's the line from the code:
colorsTables, colorsNames = colors('products', 'specificTables',
specificTables):
The syntax error is that you have an illegal colon at the end of that
line. Remove that colon.
No text. I'm just calling a function and getting the results. Here's the
pared-down function:
def colors(callingTable, which='', specificTables=[]):
The error lies in the caller of colors().
Cheers,
Chris
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Re: prolog with python
On Wed, Dec 2, 2009 at 6:47 PM, William Heath wghe...@gmail.com wrote: Hi All, I have the following prolog program that I would really like to be able to run in python in some elegant way: From googling: http://pyke.sourceforge.net/ http://code.activestate.com/recipes/303057/ Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Declaring a class level nested class?
On Wed, Dec 2, 2009 at 8:55 PM, cmckenzie mckenzi...@gmail.com wrote: Hi. I'm new to Python, but I've managed to make some nice progress up to this point. After some code refactoring, I ran into a class design problem and I was wondering what the experts thought. It goes something like this: class module: nestedClass def __init__(): self.nestedClass = nested() print self.nestedClass.nestedVar class nested(): nestedVar = 1 def __init__(self): print Initialized... I can't figure out what the correct way to construct the nested class so it can belong to module. I want a class level construct of nested to belong to module, but I keep getting nestedClass isn't defined. Here's the scoping reason why it fails (remember that the nested class is a class variable of the containing class): BEGIN PENDING FAQ SUBMISSION Why do I get errors when accessing class variables (a.k.a. static variables)? - If you try something like the following:: class Foo(object): class_variable = 42 def method(self, x): return x + class_variable Foo().method(7) You'll get an error about Python being unable to find the class variable:: Traceback (most recent call last): ... NameError: global name 'class_variable' is not defined This is because class-level scope is not consulted when looking up plain names in methods. When looking up a name, the following scopes are consulted, in order: Local variables, Variables in nested functions, Global variables, and finally, Built-ins. To refer to class variables, you must be more explicit. There are several ways to go about it: * Refer to the class by name:: def method1(self, x): return x + Foo.class_variable * Refer to the class of the object dynamically. If you class is subclassed, this will allow the subclasses to override the value of the class variable. :: def method2(self, x): return x + self.__class__.class_variable * Exploit the fact that attribute lookups on an object fall back to its class. Be warned that if you have both instance and class variables with the same name, the instance variable will shadow the class variable. :: def method3(self, x): return x + self.class_variable * If your method is not truly an instance method (i.e. does not utilize ``self``), make it a class method :: @classmethod def method4(cls, x): return x + cls.class_variable END FAQ EXCERPT However, there's pretty much no reason to nest classes anyway in Python (it's not Java!). Just make them both top-level in the file. If one class is only used internally in the module, just use the normal private naming convention of starting its name with an underscore. Also note that class names should generally use StudlyCaps, and that naming a class module is rather confusing. Cheers, Chris -- If the Python.org webmasters are listening, add the FAQ entry already! http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Help with function prototype
On Thu, Dec 3, 2009 at 3:02 AM, Nadav Chernin nada...@qualisystems.com wrote: Hi, all In past I asked about module – inspect, that can’t to get me prototype of C-implemented functions ( usually all built-in functions ). But, still I see that all Python Editors ( IDLE for example ) can to show prototype of built-in functions – by tooltip. When you print for example: sum(, you see what kind of parameters you must to enter. So, how IDLE know it? It doesn't really; it only shows the function's docstring, which /just so happens/ to document the parameters in the particular case of the built-in functions: $ python Python 2.6.2 Type help, copyright, credits or license for more information. print sum.__doc__ sum(sequence[, start]) - value Returns the sum of a sequence of numbers (NOT strings) plus the value of parameter 'start' (which defaults to 0). When the sequence is empty, returns start. type(sum.__doc__) type 'str' Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Directly converting Python to C using the C API
On Thu, Dec 3, 2009 at 6:09 PM, Emmanuel Bengio beng...@gmail.com wrote:
I'm fairly new to the python world, and I often heard critics about it's
speed, and also about it's non-compilability.
Then I thought, there is a complete C API that manages Python itself.
Would it be feasible to transform pure Python code into pure Python C API
code? It would spare the parsing time, which seems to be the an important
factor in Python's speed.
Given the following example:
x=0
for i in xrange(10):
x+=x*i
On my machine, this takes 79ms to run.
while this:
PyObject* x = PyInt_FromLong(0);
int i;
for (i=0;i10;i++)
{
x=PyNumber_Add(x,PyNumber_Multiply(x,PyInt_FromLong(i)));
}
takes about 16 ms to run.
Any thoughts?
You're going to have to check that xrange() hasn't been rebound for starters.
Cheers,
Chris
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Re: read from standard input
On Fri, Dec 4, 2009 at 9:37 PM, Siva B sivait...@gmail.com wrote:
Hi all,
I wrote a program to read some data through standard input and write in a
file.
the following code works fine in linux.
but its giving ArgumentError in windows.
There's no such error in Python; you're thinking of Ruby.
Unless you give the /actual/ error (with message) and full traceback,
there's not much we can do to help you besides just guess.
snip
file=open('data.txt','w')
Don't use `file` as a variable name, you're shadowing the built-in type.
and what is the command in windows for EOF (like Cntrl D in linux)
http://tinyurl.com/yggsby3
The *very first result* has the answer in its 6th sentence.
Cheers,
Chris
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Re: read from standard input
On Sat, Dec 5, 2009 at 11:54 AM, Chris Rebert c...@rebertia.com wrote:
On Fri, Dec 4, 2009 at 9:37 PM, Siva B sivait...@gmail.com wrote:
Hi all,
I wrote a program to read some data through standard input and write in
a
file.
the following code works fine in linux.
but its giving ArgumentError in windows.
There's no such error in Python; you're thinking of Ruby.
Unless you give the /actual/ error (with message) and full traceback,
there's not much we can do to help you besides just guess.
snip
file=open('data.txt','w')
Don't use `file` as a variable name, you're shadowing the built-in type.
and what is the command in windows for EOF (like Cntrl D in linux)
http://tinyurl.com/yggsby3
The *very first result* has the answer in its 6th sentence.
On Fri, Dec 4, 2009 at 11:13 PM, Siva B sivait...@gmail.com wrote:
Hi Chris,
Thanks for you reply.
The error log is here for my above program in windows:
Traceback (most recent call last):
File C:\Documents and Settings\user\Desktop\t1.py, line 3, in module
orig_source = sys.stdin.read()
AttributeError: read
Okay, that Shouldn't Be Happening (tm). Add the following before line
3 and post the output:
print type(sys.stdin), sys.stdin
And while we're at it, what version of Python are your running?
Cheers,
Chris
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Re: How to create a docstring for a module?
On Sun, Dec 6, 2009 at 12:34 PM, Dr. Phillip M. Feldman pfeld...@verizon.net wrote: OK. I was able to reproduce the problem. My difficulty was that the command that I issued initially was from xyz import * rather than just import xyz. If I say import xyz, then the docstring is defined; if I say from xyz import *, it isn't. I'm not sure whether this is a bug or expected behavior. Expected behavior. If you `from foo import bar`, the name `foo` won't be bound, so needless to say you won't be able to access its docstring foo.__doc__. $ ipython Python 2.6.2 (r262:71600, Nov 5 2009, 15:03:16) Type copyright, credits or license for more information. IPython 0.10 -- An enhanced Interactive Python. ? - Introduction and overview of IPython's features. %quickref - Quick reference. help - Python's own help system. object? - Details about 'object'. ?object also works, ?? prints more. In [1]: ?pickle Object `pickle` not found. In [2]: from pickle import * In [3]: ?pickle Object `pickle` not found. In [4]: pickle.__doc__ --- NameError Traceback (most recent call last) /Users/chris/ipython console in module() NameError: name 'pickle' is not defined In [5]: import pickle In [6]: ?pickle shows the documentation In [7]: pickle.__doc__ Out[7]: 'Create portable serialized representations of Python objects.\n\nSee module cPickle for a (much) faster implementation.\nSee module copy_reg for a mechanism for registering custom picklers.\nSee module pickletools source for extensive comments.\n\nClasses:\n\nPickler\nUnpickler\n\nFunctions:\n\n dump(object, file)\ndumps(object) - string\nload(file) - object\nloads(string) - object\n\nMisc variables:\n\n __version__\nformat_version\ncompatible_formats\n\n' Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: dict.fromkeys strange behavior
On Mon, Dec 7, 2009 at 12:42 AM, Tsviki Hirsh tsviki.hi...@gmail.com wrote:
Dear list,
I'm trying to create a dictionary from set of keys and values using
dict.fromkeys
When I type:
dict.fromkeys('a',50)
the output is:
{'a': 50}
This is fine, but when I try to set the same value to a different name key:
dict.fromkeys('at',50)
the output now is:
{'a': 50, 't': 50}
This is obviously not what I wanted.
What are the alternatives?
dict.fromkeys(['at'],50)
{'at': 50}
Remember that strings are collections too (of individual characters).
Cheers,
Chris
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Re: hola
2009/12/6 franki fuentes cueto ffrankis...@gmail.com: hola soy un pequeño programador y quiesiera pedirles ayuda para programar en python, no se si me podrian mandar ejemplos para poder empezar, y como terminarlo para que se ejecute, me entiendes , aver sime ayudan gracias Esta lista de discusión es en Inglés. Hay una lista de discusión en Español aqui: http://listas.aditel.org/listinfo/python-es Salud, Chris -- Sé solamente un poquito de Español. http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: switch
On Tue, Dec 8, 2009 at 5:53 PM, hong zhang henryzhan...@yahoo.com wrote: Python does not have switch statement. Any other option does similar work? Yes, a dictionary with functions as values: http://simonwillison.net/2004/May/7/switch/ Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Generating diagrams from PostgreSQL with Python (Re: postgresql_autodoc in Python?)
On Thu, Dec 10, 2009 at 3:48 AM, Diez B. Roggisch de...@nospam.web.de wrote: Wolfgang Keller wrote: Hello, I will re-precise my question: Has anyone ever implemented a script in Python that generates documentation (especially diagrams, in a format such as e.g. Dia, Inkscape SVG or Tikz) for a PostgreSQL database either from an SQL script or by connecting to the database? I've written a schemadiff-tool for postgres based on SQLAlchemy reflection, which is a branch of SQLAlchemy and which should become part of the upcoming SA 0.6. http://svn.sqlalchemy.org/sqlalchemy/branches/reflection It allows you to extract information about the schema of the DB. This could be the foundation of your tool. Postgresql_autodoc is unfortunately written in Perl. ;- TIA, And, btw., please respect my .sig, Which is supposed to mean what? Never heard the term courtesy copy. It appears to be an incorrect expansion of Cc, which is actually Carbon copy. Apparently he means all replies should be directly to the list and not Cc his individual email address. Which seems strange, because usually mailinglists are smart enough not to send the author duplicate copies if they're named in the To or Cc fields. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: read text file byte by byte
On Sun, Dec 13, 2009 at 12:20 AM, Michel Claveau - MVP enleverlesx_xx...@xmclavxeaux.com.invalid wrote: Hi! If it's a binary file... OK, but... what is a binary file? http://en.wikipedia.org/wiki/Binary_file Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: unable to read the __main__ namespace
On Sun, Dec 13, 2009 at 3:20 AM, vsoler vicente.so...@gmail.com wrote: I'm learning Python, and I am very fond of it. Using Python 2.6 I am able to list all the names in a class namespace: class abc: pass abc.a1=7 abc.a2='Text' print abc.__dict__.keys() That is more simply written as: print dir(abc) a) However, I do not know how to read the __main__ namespace print __main__.__dict__.keys() # Just does not work __main__ is not used or set and has no special meaning to the Python interpreter. It's true that __name__ == __main__ in the body of the main module, but you can't actually access it by that name. b) How do i read an imported module namespace? import module print dir(module) c) How could I possibly list the names and contents of the namespace of my python session? print dir() I'd advise reading the docs on it: http://docs.python.org/library/functions.html#dir Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: insert unique data in a list
On Sun, Dec 13, 2009 at 5:19 PM, knifenomad knifeno...@gmail.com wrote: On 12월14일, 오전2시57분, mattia ger...@gmail.com wrote: Il Sun, 13 Dec 2009 16:37:20 +, mattia ha scritto: How can I insert non-duplicate data in a list? I mean, is there a particular option in the creation of a list that permit me not to use something like: def append_unique(l, val): if val not in l: l.append(val) Ok, so you all suggest to use a set. Now the second question, more interesting. Why can't I insert a list into a set? I mean, I have a function that returns a list. I call this function several times and maybe the list returned is the same as another one already returned. I usually put all this lists into another list. How can I assure that my list contains only unique lists? Using set does'n work (i.e. the python interpreter tells me: TypeError: unhashable type: 'list')... this makes the set type hashable. class Set(set): __hash__ = lambda self: id(self) Or you could just use frozenset and get the correct semantics: http://docs.python.org/library/stdtypes.html#frozenset Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: dictionary with tuple keys
On Mon, Dec 14, 2009 at 9:49 PM, Brandon Devine your.mas...@gmail.com wrote: Hi all, I am probably not thinking straight anymore about this problem. I have a dictionary with tuple keys in the format (a, b, A, B) and float values. I want to collect all the keys with identical (a, b...), disregarding whatever (... A, B) might be. Specifically, I want to sum the float values once I've collected these keys. I am staring at my screen, pondering ugly things, and I just know I must be missing a Pythonic solution. Any suggestions? from collections import defaultdict new_dict = defaultdict(int) for tupkey in your_dict: new_key = tupkey[:2] new_dict[new_key] += your_dict[tupkey] Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: csv reader
On Tue, Dec 15, 2009 at 1:24 PM, Emmanuel manou...@gmail.com wrote: I have a problem with csv.reader from the library csv. I'm not able to import accentuated caracters. For example, I'm trying to import a simple file containing a single word equação using the following code: import csv arquivoCSV='test' a=csv.reader(open(arquivoCSV),delimiter=',') tab=[] for row in a: tab.append(row) print tab As a result, I get: [['equa\xe7\xe3o']] How can I solve this problem? From http://docs.python.org/library/csv.html : Note: This version of the csv module doesn’t support Unicode input. Also, there are currently some issues regarding ASCII NUL characters. Accordingly, all input should be UTF-8 or printable ASCII to be safe; see the examples in section Examples. These restrictions will be removed in the future. Thus, you'll have to decode the results into Unicode manually; this will require knowing what encoding your file is using. Files in some encodings may not parse correctly due to the aforementioned NUL problem. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Odd json encoding erro
On Tue, Dec 15, 2009 at 2:03 PM, Wells thewellsoli...@gmail.com wrote:
I get this exception when decoding a certain JSON string:
'ascii' codec can't encode character u'\u2019' in position 8: ordinal
not in range(128)
The JSON data in question:
http://mlb.com/lookup/json/named.player_info.bam?sport_code=%27mlb%27player_id=%27489002%27
It's in the 'high_school' key. Is there some string function I can run
on the information before I decode it to avoid this?
From what I can guess (you didn't include any code), you're printing
the result of loading the JSON (which probably loaded correctly) to
the terminal without specifying the exact encoding to use. In such
cases, Python defaults to ASCII. However, your data obviously includes
non-ASCII characters, thus resulting in the error you're encountering.
Instead of `print the_high_school`, try `print
the_high_school.encode('utf8')`.
Note that the `json` library returns Unicode strings of the type
`unicode` and not byte strings of type `str` (unless you're using
Python 3.0, in which case `unicode` got renamed to `str` and `str` got
renamed to `bytes`). When outputting Unicode, it needs to be encoded
to bytes. The built-in type() function* can help determine when you
have Unicode data.
Cheers,
Chris
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*Yes, it's not /really truly/ a function, but the distinction is not
relevant here.
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Re: Odd json encoding erro
On Tue, Dec 15, 2009 at 3:04 PM, Wells thewellsoli...@gmail.com wrote:
Sorry- more detail- the actual problem is an exception thrown when
running str() on the value, like so:
a = u'St. Paul\u2019s School For Boys (MN) HS'
print str(a)
Traceback (most recent call last):
File stdin, line 1, in module
UnicodeEncodeError: 'ascii' codec can't encode character u'\u2019' in
position 8: ordinal not in range(128)
Is there some way to run str() against a unicode object?
To repeat what I said earlier, you use the .encode() method instead:
print a.encode('utf8')
Might I recommend reading:
http://www.joelonsoftware.com/articles/Unicode.html
Regards,
Chris
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Re: strptime not strict enough
On Tue, Dec 15, 2009 at 9:47 PM, Tim Roberts t...@probo.com wrote:
Tobias Weber t...@gmx.net wrote:
despite the directives for leading zero stime.strptime('09121',
'%y%m%d') returns the first of December. Shouldn't it raise ValueError?
Python merely calls the strptime function in your C run-time library. If
it sucks, so will time.strptime.
Er, no, wrong:
http://svn.python.org/view/python/trunk/Lib/_strptime.py?view=markup
Cheers,
Chris
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Re: Storing a Value in a Cookie
On Wed, Dec 16, 2009 at 1:13 AM, Victor Subervi victorsube...@gmail.com wrote: Hi; From what I've studied and gotten working about cookies, it seems one can store only a certain few pieces of information--expiration, path, comment, domain, max-age, version and last visit--but how is it useful if one can't also store, say, the name of a temporary MySQL table where pertinent customer data, such as shopping cart data, is stored? I guess I could put that into the comment field, but I suspect there's a better way of doing it. Please advise. Besides the metadata you mentioned, a cookie can also store one key-value pair, which is sent as the first part of the Cookie HTTP header when setting the cookie (Cookie: name=value); this is typically used to store a session ID. It is inadvisable to store much data other than a session ID in a cookie because as a rule, in order to avoid security risks, clients should not be trusted. In the example you give of storing the name of an SQL table, someone could guess the name of another user's SQL table and alter their cookie to masquerade as that user, thus compromising the other customer's shopping cart, and depending on the contents of the SQL table, potentially their credit card. Most web frameworks, like Django, will handle low-level details like setting and getting cookies for you and provide a higher-level API for dealing with sessions and/or users. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Can't Iterate
On Wed, Dec 16, 2009 at 11:26 PM, Victor Subervi
victorsube...@gmail.com wrote:
Hi;
I have this line of code:
for store in ourStores():
which is called from the statement:
from particulars import ourStores
The latter file has the following:
def ourStores():
return ['prescriptions', 'products']
Yet, the above iteration only iterates the last of these items ('products').
Why?
To put it mildly: Unable to reproduce the problem.
Post a more complete code sample. For instance, include whatever
debugging code is leading you to believe that only products is being
yielded by the iteration.
Cheers,
Chris
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Re: py itertools?
On Sat, Dec 19, 2009 at 2:54 AM, mattia ger...@gmail.com wrote:
Hi all, I need to create the permutation of two strings but without
repeat the values, e.g. 'ab' for me is equal to 'ba'. Here is my
solution, but maybe the python library provides something better:
def mcd(a, b):
... if b == 0:
... return a
... else:
... return mcd(b, a % b)
...
def mcm(a, b):
... return int((a * b) / mcd(a, b))
...
s1 = 'abc'
s2 = 'wt'
m = mcm(len(s1), len(s2))
set(zip(s1*m, s2*m))
{('a', 'w'), ('a', 't'), ('b', 'w'), ('c', 't'), ('b', 't'), ('c', 'w')}
Any help?
Surprised you didn't think of the seemingly obvious approach:
def permute_chars(one, two):
for left in set(one):
for right in set(two):
yield (left, right)
list(permute_chars('abc', 'wt'))
[('a', 'w'), ('a', 't'), ('b', 'w'), ('b', 't'), ('c', 'w'), ('c', 't')]
Cheers,
Chris
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Re: Class variables static by default?
On Sat, Dec 19, 2009 at 8:16 PM, Steven D'Aprano st...@remove-this-cybersource.com.au wrote: On Sun, 20 Dec 2009 11:44:11 +1100, Lie Ryan wrote: In python, 'class variable' is a variable that belongs to a class; not to the instance and is shared by all instance that belong to the class. Surely, since string variables are strings, and float variables are floats, and bool variables are bools, and module variables are modules, a class variable will be a class and an instance variable will be an instance? As they say, the exception proves the rule. :) Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Something Like os.environ['HTTP_REFERER']
On Sun, Dec 20, 2009 at 2:06 AM, Victor Subervi victorsube...@gmail.com wrote: Hi; I'm looking for something like os.environ['HTTP_REFERER'] but for python scripts. That is, if I have a script that is imported by another script, how can I have the script that is being imported determine which script imported it? Allow me to ask the meta-question of: Why do you want to do that? There is quite possibly a better means to accomplish whatever end you have. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Mails encoding
On Sun, Dec 20, 2009 at 2:46 AM, Lord Eldritch lord_eldri...@yahoo.co.uk wrote: snip - When I have: ttext='áá' I get a warning sendinme to this page http://www.python.org/peps/pep-0263.html Should I understand that PEP has been already implemented and follow it? Yes. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Import Problem
On Sun, Dec 20, 2009 at 3:34 AM, Victor Subervi victorsube...@gmail.com wrote: snip But I get this error: /var/www/html/angrynates.com/cart/createTables2.py 263 /html 264 ''' 265 266 createTables2() 267 createTables2 = function createTables2 /var/www/html/angrynates.com/cart/createTables2.py in createTables2() 105 these.append(basic) 106 i = 0 107 specialtyStore = addStore() 108 addStore = [] Rename this list so its name isn't the same as the addStore() function which you call. For more info, see: http://groups.google.com/group/comp.lang.python/browse_thread/thread/46b4c8af3196caaa?pli=1 109 addStore.append(specialtyStore) specialtyStore undefined, global addStore = function addStore UnboundLocalError: local variable 'addStore' referenced before assignment args = (local variable 'addStore' referenced before assignment,) Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: py itertools?
On Dec 19, 12:48 pm, Chris Rebert c...@rebertia.com wrote:
On Sat, Dec 19, 2009 at 2:54 AM, mattia ger...@gmail.com wrote:
Hi all, I need to create the permutation of two strings but without
repeat the values, e.g. 'ab' for me is equal to 'ba'. Here is my
solution, but maybe the python library provides something better:
def mcd(a, b):
... if b == 0:
... return a
... else:
... return mcd(b, a % b)
...
def mcm(a, b):
... return int((a * b) / mcd(a, b))
...
s1 = 'abc'
s2 = 'wt'
m = mcm(len(s1), len(s2))
set(zip(s1*m, s2*m))
{('a', 'w'), ('a', 't'), ('b', 'w'), ('c', 't'), ('b', 't'), ('c', 'w')}
Any help?
Surprised you didn't think of the seemingly obvious approach:
def permute_chars(one, two):
for left in set(one):
for right in set(two):
yield (left, right)
list(permute_chars('abc', 'wt'))
[('a', 'w'), ('a', 't'), ('b', 'w'), ('b', 't'), ('c', 'w'), ('c', 't')]
On Sun, Dec 20, 2009 at 3:21 AM, Parker xeno...@gmail.com wrote:
a = 'qwerty'
b = '^%$#'
c = [(x,y) for x in a for y in b]
c
[('q', '^'), ('q', '%'), ('q', ''), ('q', '$'), ('q', '#'), ('w',
'^'), ('w', '%'), ('w', ''), ('w', '$'), ('w', '#'), ('e', '^'),
('e', '%'), ('e', ''), ('e', '$'), ('e', '#'), ('r', '^'), ('r',
'%'), ('r', ''), ('r', '$'), ('r', '#'), ('t', '^'), ('t', '%'),
('t', ''), ('t', '$'), ('t', '#'), ('y', '^'), ('y', '%'), ('y',
''), ('y', '$'), ('y', '#')]
This one is better and simple.
But fails if either of the input strings has repeated characters.
(Although writing it as a comprehension is indeed much briefer.)
Whether this matters, who knows, since the OP's spec for the function
was rather vague...
Cheers,
Chris
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Re: Create attribute from string
On Wed, Dec 30, 2009 at 9:22 PM, AON LAZIO aonla...@gmail.com wrote: Hi, I would like to know how we could create attribute from string say I want to assign value 0.05 to an object attribute I like to input SIGNIFICANT and 0.05 and get object.SIGFICANT equals to 0.05 setattr(obj, SIGNIFICANT, 0.05) Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Exception as the primary error handling mechanism?
On Thu, Dec 31, 2009 at 8:47 PM, Peng Yu pengyu...@gmail.com wrote: I observe that python library primarily use exception for error handling rather than use error code. In the article API Design Matters by Michi Henning Communications of the ACM Vol. 52 No. 5, Pages 46-56 10.1145/1506409.1506424 http://cacm.acm.org/magazines/2009/5/24646-api-design-matters/fulltext It says Another popular design flaw—namely, throwing exceptions for expected outcomes—also causes inefficiencies because catching and handling exceptions is almost always slower than testing a return value. My observation is contradicted to the above statement by Henning. If my observation is wrong, please just ignore my question below. Otherwise, could some python expert explain to me why exception is widely used for error handling in python? Is it because the efficiency is not the primary goal of python? Correct; programmer efficiency is a more important goal for Python instead. Python is ~60-100x slower than C;[1] if someone is worried by the inefficiency caused by exceptions, then they're using completely the wrong language. Cheers, Chris -- http://blog.rebertia.com [1] http://shootout.alioth.debian.org/u64/which-programming-languages-are-fastest.php?gcc=onpython=oncalc=chart -- http://mail.python.org/mailman/listinfo/python-list
Re: Significant whitespace
On Fri, Jan 1, 2010 at 2:02 PM, Dan Stromberg drsali...@gmail.com wrote: I put together a page about significant whitespace (and the lack thereof). You're invited to check it out: http://stromberg.dnsalias.org/~dstromberg/significant-whitespace.html For those of us who weren't around during the heyday of FORTRAN, can anyone describe this apparently much-reviled significant whitespace feature that continues to make some programmers unjustly fearful about Python's use of indentation? Thanks in advance. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Significant whitespace
On Fri, Jan 1, 2010 at 9:56 PM, Donn donn.in...@gmail.com wrote: On Saturday 02 January 2010 00:02:36 Dan Stromberg wrote: I put together a page about significant whitespace (and the lack thereof). The only thing about Python's style that worries me is that it can't be compressed like javascript can*, and perhaps that will prevent it becoming a browser-side language one day. How I'd love to code PyQuery instead of JQuery! * Or am I wrong? Not to my knowledge, but CPython's bytecode format could be used to similar effect. However, the larger and much more daunting obstacle to client-side Python would be that it's not sandboxed or secured like JavaScript is, although there are some people working on it. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: TypeError: can only concatenate list (not tuple) to list
On Sun, Jan 3, 2010 at 11:51 PM, Gabriel Genellina gagsl-...@yahoo.com.ar wrote: This py [1,2,3] + (4,5) Traceback (most recent call last): File stdin, line 1, in module TypeError: can only concatenate list (not tuple) to list Given that tuples are sometimes used as a poor man's object (i.e. collection of data fields), whereas lists are not typically used that way, I'd say it's probably a good thing an explicit type conversion is required here. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Can't Add Variable
On Mon, Jan 4, 2010 at 9:28 AM, Victor Subervi victorsube...@gmail.com wrote: Hi; I have this code snippet: sql '''create table if not exists %sCustomerData ( You're missing an equal sign there to start with (i.e. sql = '''). Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: How to validate the __init__ parameters
On Mon, Jan 4, 2010 at 10:17 AM, Albert van der Horst alb...@spenarnc.xs4all.nl wrote: snip This triggers a question: I can see the traceback, but it would be much more valuable, if I could see the arguments passed to the functions. Is there a tool? print(locals()) #this actually gives the bindings for the entire local namespace #but is less work than writing something more precise by hand. It is amazing how handy the humble print() function/statement is when debugging. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Newbie help- Can multiple instances with multiple names automatically created.
On Mon, Jan 4, 2010 at 1:32 PM, Shawn Milochik sh...@milochik.com wrote:
You could put them in a dictionary with the key being the name, instead of a
list.
To illustrate that for the OP:
name2drink = {}
for booze in liquors:
for juice in juices:
name = juice + +booze # or however you're naming them
drink = Bottle(booze, juice)
name2drink[name] = drink
#example use
favorite = name2drink[apple wine]
favorite.rating = 9/10
Cheers,
Chris
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Re: Exception as the primary error handling mechanism?
much snippage On Tue, Jan 5, 2010 at 1:07 AM, r0g aioe@technicalbloke.com wrote: Lie Ryan wrote: I have been looking at Haskell recently and the way the pure functional language handled exceptions and I/O gives me a new distinct insight that exceptions can be thought of as a special return value that is implicitly wrapped and unwrapped up the call stack until it is explicitly handled. Yes there's some very interesting paradigms coming out of functional programming but, unless you're a maths major, functional languages are a long way off being productivity tools! Elegant: yes, provable: maybe, practical for everyday coding: not by a long shot! Methinks the authors of Real World Haskell (excellent read btw) have a bone to pick with you. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Exception as the primary error handling mechanism?
On Tue, Jan 5, 2010 at 3:51 PM, Phlip phlip2...@gmail.com wrote:
Peng Yu wrote:
Otherwise, could some python expert explain to me why exception is
widely used for error handling in python? Is it because the efficiency
is not the primary goal of python?
It's not about efficiency, it's about making assumptions for the
programmer about what kind of rigor they need.
Why can't int('nonnumeric') return None?
Errors should never pass silently.
Unless explicitly silenced.
-- The Zen of Python (http://www.python.org/dev/peps/pep-0020/)
Better to throw an exception and ensure the case is specifically dealt
with one way or another than to silently return an error flag result
which may only delay the error until later in the program, making it
harder to debug. Is it that much of a burden to write and use the
small function that does what you want?
def int_or_None(string):
try:
return int(string)
except ValueError:
return None
Heck, you can even write it inline and dispense with the function if you want:
try: foo = int(bar)
except ValueError: foo = None
Quibbling over a mere one more line of code (or writing one short
function) seems a bit petty.
(A related question - why can't I just go 'if record = method(): use
(record)'. Why extra lines just to trap and assign the variable before
using it?)
I believe that's disallowed so as to prevent the subtle bugs seen in C
code which result from when someone makes a typo and omits the second
= in their `if foo == bar():` test.
Cheers,
Chris
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Re: Exception as the primary error handling mechanism?
On Tue, Jan 5, 2010 at 5:45 PM, Phlip phlip2...@gmail.com wrote:
On Jan 5, 5:01 pm, Chris Rebert c...@rebertia.com wrote:
Why can't int('nonnumeric') return None?
Errors should never pass silently.
You are saying I, as the programmer, cannot decide what is an error
and what is a pass-thru. The decision is made for me. (Yes yes I can
write int_or_None(), etc...)
No, you can certainly decide yourself. You merely need be explicit
about it; you're leaving out the other tandem half of the couplet:
*Unless* explicitly silenced. Throwing exceptions is only the
default because it tends to lead to more reliable code in that you're
forced to deal with the error condition by either catching an
exception or preventing one from being thrown (by, say, using a
different method in the API that just returns a default value
instead).
As an aside, I would guess the built-in types don't have default value
parameters for conversions partly because it'd be a bit less elegant
to implement; since None is a commonly used default value, they'd have
to use a different sentinel as said parameter's default value to
indicate that the caller wanted an exception raised, and having a
hierarchy of nil values in the core language detracts from the
language's elegance.
At any rate, if you like dict.get(), I don't see why, say,
my_int('nonnumeric', None) should be such a problem.
Here's a super easy example:
{ 42: 'forty two' }.get(41, None)
Because I can supply a default, I can decide what is an error and what
is .
Exactly, that's explicitly silencing the error; no one ever said an
`except` clause was the only silencing mechanism. You're making your
intention clear by using .get() and passing in a desired default. I
agree this is a fine thing.
Now the equivalent in a language that does not enjoy this false Zen:
{ 42: 'forty two' }[41] # returns None
{ 42: 'forty two' }.fetch(41, None) # ibid
{ 42: 'forty two' }.fetch(41) # raises an exception
The quicky validation is available if I _request_ it.
Seems like rather fast-and-loose programming if you don't care about
validation enough of the time to merit it being default. If your
programming is indeed so fast-and-loose, I refer you to the recent
comment about PHP (and other less exception-happy languages).
Anyway, I do totally agree that you should, if feasible, be provided
an easy way to designate a common error-handling strategy (for
example, in this case, by using a default value via .fetch()).
However, go too loose on error handling and exceptions and one ends up
with something like JavaScript with its infamous `undefined` value
which can make debugging a nightmare (whoever came up with the idea of
JS's `undefined` should be slapped upside the head).
Cheers,
Chris
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Re: buffer interface problem
On Thu, Jan 7, 2010 at 12:19 AM, Andrew Gillanders andrew.gilland...@uqconnect.edu.au wrote: I have run into a problem running a Python script that is part of the TerraGear suite for building scenery for FlightGear. I am using Mac OS X 10.4, running Python (version 3.0.1) in a Unix terminal. The purpose of the script is to walk a directory tree, unzipping files, and passing the contents to an executable C program. The problem occurs here: gzin = GzipFile(fname, 'rb') data = gzin.readline() min_x,min_y = map(atoi,data.split()[:2]) The input file, when uncompressed, is an ASCII file with a line with two numbers, then a line of four numbers, then many long lines of numbers. I can see what the last is trying to do: split the string into two words, convert them to integers, and assign them to min_x and min_y. At the third line, I get the message expected an object with the buffer interface. Which object is it referring to? The elements of the list produced by `data.split()[:2]`, which are either Unicode strings or bytestrings, neither of which are buffers. Have some functions been changed to pass buffer objects instead of strings? How can I fix the source code to make it run? The error is being raised by the atoi() function (in the future, please post the full Traceback, not just the final error message). What module/library does your atoi() function come from (look for an `import` statement mentioning it)? The only functions by that name in the Python standard library both operate on strings, not buffers, and thus can't be the same one your code is using. In any case, replacing `atoi` with `int` in your code will likely solve the problem. The built-in int() function* can convert strings to integers. Cheers, Chris -- http://blog.rebertia.com *Not really a function, but close enough for newbie explanatory purposes. -- http://mail.python.org/mailman/listinfo/python-list
Re: buffer interface problem
On Thu, Jan 7, 2010 at 4:47 AM, Andrew Gillanders
andrew.gilland...@uqconnect.edu.au wrote:
On 07/01/2010, at 7:13 PM, Chris Rebert wrote:
On Thu, Jan 7, 2010 at 12:19 AM, Andrew Gillanders
andrew.gilland...@uqconnect.edu.au wrote:
I have run into a problem running a Python script that is part of the
TerraGear suite for building scenery for FlightGear. I am using Mac OS X
10.4, running Python (version 3.0.1) in a Unix terminal.
The purpose of the script is to walk a directory tree, unzipping files,
and
passing the contents to an executable C program. The problem occurs here:
gzin = GzipFile(fname, 'rb')
data = gzin.readline()
min_x,min_y = map(atoi,data.split()[:2])
The input file, when uncompressed, is an ASCII file with a line with two
numbers, then a line of four numbers, then many long lines of numbers. I
can
see what the last is trying to do: split the string into two words,
convert
them to integers, and assign them to min_x and min_y.
At the third line, I get the message expected an object with the buffer
interface. Which object is it referring to?
The elements of the list produced by `data.split()[:2]`, which are
either Unicode strings or bytestrings, neither of which are buffers.
Have some functions been
changed to pass buffer objects instead of strings? How can I fix the
source
code to make it run?
The error is being raised by the atoi() function (in the future,
please post the full Traceback, not just the final error message).
What module/library does your atoi() function come from (look for an
`import` statement mentioning it)?
The only functions by that name in the Python standard library both
operate on strings, not buffers, and thus can't be the same one your
code is using.
In any case, replacing `atoi` with `int` in your code will likely
solve the problem. The built-in int() function* can convert strings to
integers.
Thanks Chris. The atoi function was coming from the locale library (from
locale import atoi). I changed it to int and now it works.
Hm, that's odd since it was one of the 2 functions in the std lib
which the docs say operates on strings...
The next hurdle is this:
gzin = GzipFile(fname, 'rb')
data = gzin.readline()
#min_x,min_y = map(atoi,data.split()[:2])
min_x,min_y = map(int,data.split()[:2])
data = gzin.readline()
#span_x,step_x,span_y,step_y = map(atoi,data.split()[:4])
span_x,step_x,span_y,step_y = map(int,data.split()[:4])
data = gzin.read().split('\n')
The last line is a problem, giving me this message: Type str doesn't support
the buffer API (I am guessing a conflict between split and read?)
Ah, looking at the 3.0 docs on buffers, I'd surmise gzin.read()
returns bytes (http://docs.python.org/3.1/library/functions.html#bytes)
rather than a string.
You'll want to decode the bytes into characters first, and then you
can operate on the resulting string normally.
Try:
data = gzin.read().decode('ascii').split('\n')
Sorry, I am new to Python, so how do I get a Traceback?
You should get one by default. Are you running the script in some
environment other than the command line?
Here's what a traceback looks like:
Traceback (most recent call last):
File foo, line 161, in module
main()
File foo.py, line 157, in main
bot.run()
File foo.py, line 68, in bar
self.baz(Enter number: )
File foo.py, line 112, in baz
choice = int(raw_input(prompt))-1
ValueError: invalid literal for int() with base 10: 'y'
Cheers,
Chris
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Re: Recommended new way for config files
On Thu, Jan 7, 2010 at 10:19 AM, Peter vm...@mycircuit.org wrote: snip The .ini file is the simpliest solution, at least from the user point of view, no need to learn any python syntax. I am speaking from the point of view of a python programmer, and I find the .ini restrictions not necessarily simple, for example when dealing with structured data (I suppose it is trivial to specify a dictionnary or a list for the purpose of my request) For example, configuration files for the logging module get unwieldy when you specify several loggers , handlers, formatters etc, because you have to break down structured data ( objects ) to name,value pairs. snip So what is the worshipped approach, when you need more than name=value pairs ? JSON is one option: http://docs.python.org/library/json.html Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Standardized interpreter speed evaluation tool
On Fri, Jan 8, 2010 at 2:25 AM, alexru tara...@gmail.com wrote: Is there any standardized interpreter speed evaluation tool? Say I made few changes in interpreter code and want to know if those changes made python any better, which test should I use? Although apparently undocumented, test.pystone is some sort of interpreter benchmark. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: integer and string compare, is that correct?
On Sun, Jan 10, 2010 at 4:26 AM, Hellmut Weber m...@hellmutweber.de wrote: Hi, being a causal python user (who likes the language quite a lot) it took me a while to realize the following: l...@sylvester py_count $ python Python 2.6.3 (r263:75183, Oct 26 2009, 12:34:23) [GCC 4.4.1] on linux2 Type help, copyright, credits or license for more information. max = '5' n = 5 n = max False n + max Traceback (most recent call last): File stdin, line 1, in module TypeError: unsupported operand type(s) for +: 'int' and 'str' Section 5.9 Comparison describes this. Can someone give me examples of use cases The behavior of disparate types being comparable is deprecated and has been removed in Python 3.0+; don't rely upon it. (The ordering used is arbitrary but consistent) IIRC, the feature existed in prior versions to make lists containing mixed types sortable; this was found to be not all that useful and to hide what are quite arguably errors. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: integer and string compare, is that correct?
On Sun, Jan 10, 2010 at 4:46 AM, Chris Rebert c...@rebertia.com wrote: snip The behavior of disparate types being comparable is deprecated and has been removed in Python 3.0+; don't rely upon it. Clarification: Equality testing between disparate types still works unaltered however. By comparable, I meant , , =, = comparisons. Cheers, Chris -- http://mail.python.org/mailman/listinfo/python-list
Re: how to duplicate array entries
On Sun, Jan 10, 2010 at 10:21 PM, Sebastian sebastian.lan...@gmx.de wrote: Hi there, I have an array x=[1,2,3] Is there an operator which I can use to get the result [1,1,1,2,2,2,3,3,3] ? I tried x*3, which resulted in [1,2,3,1,2,3,1,2,3] I also tried [[b,b,b] for b in x] which led to [[1,2,3],[1,2,3], [1,2,3]], but this isn't what I want either. from itertools import chain, repeat n = 3 stretched = list(chain(*[repeat(item, n) for item in x])) Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: how to duplicate array entries
On Mon, Jan 11, 2010 at 1:03 AM, Alf P. Steinbach al...@start.no wrote: * Steven D'Aprano: On Mon, 11 Jan 2010 08:56:36 +0100, Alf P. Steinbach wrote: * Paul Rudin: Sebastian sebastian.lan...@gmx.de writes: I have an array x=[1,2,3] In python such an object is called a list. (In cpython it's implemented as an automatically resizable array.) I don't think the OP's terminology needs correction. A Python list is an array functionality-wise. If one isn't observant of that fact then one ends up with O(n^2) time for the simplest things. Well that's certainly not true. Some operations may be O(N**2), but others are not: list.append() is amortized O(N) and for individual appends, may be can be as fast as O(1). The second sentence may or may not be true. I don't know of any fundamental 'list' operations that have quadratic time. Is there? The first sentence is just baffling -- what on Earth is the that that you think is not true? OK, I can guess (correct me if I'm guessing wrong, please): you think I'm talking about elementary operations. I'm not. I'm talking about algorithmic complexity for loops doing e.g. insertions. Using the term array accentuates and clarifies this most important aspect. But Python lists are designed to behave as lists. No, I'm sorry, they're not. A Python 'list' has de facto constant time indexing, or random access. A linked list -- what the informal list means in programming Eh, it's a bit context-dependent. The abstract data type definition is a superset that includes both linked lists and dynamic arrays. FWIW, Java likewise uses list in its ADT sense. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: how to duplicate array entries
On Mon, Jan 11, 2010 at 2:20 AM, Alf P. Steinbach al...@start.no wrote: * Chris Rebert: On Mon, Jan 11, 2010 at 1:03 AM, Alf P. Steinbach al...@start.no wrote: * Steven D'Aprano: On Mon, 11 Jan 2010 08:56:36 +0100, Alf P. Steinbach wrote: * Paul Rudin: Sebastian sebastian.lan...@gmx.de writes: snip Using the term array accentuates and clarifies this most important aspect. But Python lists are designed to behave as lists. No, I'm sorry, they're not. A Python 'list' has de facto constant time indexing, or random access. A linked list -- what the informal list means in programming Eh, it's a bit context-dependent. The abstract data type definition is a superset that includes both linked lists and dynamic arrays. Assuming you're talking about some abstract type definition that's in some PEP somewhere No, I mean the computer science definition/term: http://en.wikipedia.org/wiki/List_(computer_science) FWIW, Java likewise uses list in its ADT sense. I'm sorry, I'm unfamiliar with that Java terminology (but then, reportedly, many Java programmers think that Java has pass by reference, so nothing coming from that direction will surprise me very much!). The Java language specification has a section about arrays, none about lists AFAICS. Do you have a reference? http://java.sun.com/j2se/1.4.2/docs/api/java/util/List.html Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: os.system function
On Mon, Jan 11, 2010 at 12:43 PM, Zabin zabin.faris...@gmail.com wrote: Hey everyone! I am a new python programmer. I am trying to get the general file functionality with options of save and save as working. These save functions save a folder with multiple files. Upon using the os.system copy function- if my destination directory has files with similar names- i am asked whether i want to replace the files on the command prompt. Is there some way of getting this question into a dialog box? Also is there someway of avoiding or programmatically setting the response to the command prompt? You can probably avoid using os.system() entirely (always a good thing) by instead using the functions in the `shutil` library: http://docs.python.org/library/shutil.html And for future reference, the `subprocess` module is the preferred way to invoke external programs, rather than os.system(): http://docs.python.org/library/subprocess.html Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: What is built-in method sub
On Mon, Jan 11, 2010 at 12:34 PM, Steven D'Aprano st...@remove-this-cybersource.com.au wrote: snip If you can avoid regexes in favour of ordinary string methods, do so. In general, something like: source.replace(target, new) will potentially be much faster than: regex = re.compile(target) regex.sub(new, source) # equivalent to re.sub(target, new, source) (assuming of course that target is just a plain string with no regex specialness). If you're just cracking a peanut, you probably don't need the 30 lb sledgehammer of regular expressions. Of course, but is the regex library really not smart enough to special-case and optimize vanilla string substitutions? Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: os.system function
On Mon, Jan 11, 2010 at 2:00 PM, Zabin zabin.faris...@gmail.com wrote: snip and just wondering- whats the drawback of using os.system() command Forgetting to properly escape your input. Simple example: filename = foo bar.txt os.system(rm +filename) # uh-oh, we deleted 'foo' and 'bar.txt' instead The `subprocess` module makes escaping unnecessary. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Python File Search
2010/1/11 Eknath Venkataramani eknath.i...@gmail.com:
correct.txt snippet:
1 2 1
1 3 3
1 5 21
1 7 19
union_output_TEMP.txt snippet:
1 2 1_NN
1 3 3_VBZ
1 3 5_VBZ
1 3 2_VBZ
1 5 21_VB
1 7 19_NN
1 9 14_VB
I need to get the output in categorized.txt as:
NN={1 7 19, 1 2 1}
VBZ={1 3 3}
VB={1 5 21}
in python.
Kindly help
We don't do other's homework
(http://in.linkedin.com/pub/eknath-venkataramani/17/1a9/b55), but are
willing to give hints.
I would give a more clear explanation of what this is supposed to do
if you want useful advice.
For example, why does NN contain all matching entries when the other 2
only include the first matching entries?
Cheers,
Chris
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Re: A question about Python versions
On Tue, Jan 12, 2010 at 10:09 PM, Gib Bogle g.bo...@auckland.no.spam.ac.nz wrote: I am learning Python, and using PyQt to develop a GUI that will be used to run a Fortran program on Windows, Linux and Mac OS X (I think Python is great, btw). Without thinking about it I downloaded and started working with a fairly recent Python version, 2.5.4. I've now become aware of the existence of Python 3.1, which apparently is a major revision of the language. Does it make sense to stick with Python 2.x at this point, or should I be starting off with 3.1? This is an FAQ, so you can search the archives for many other responses. If your program needs to use any third-party libraries besides PyQt, you should probably use 2.x as most libraries have yet to be ported to 3.x yet (luckily, PyQt apparently has been ported already). If your program will be pretty self-sufficient, Python 3 is definitely an option and will be nicer to use thanks to the improvements to the language, but most of the changes (aside from strings becoming Unicode) aren't dramatic; it is clearly still the same language (unlike Perl 5 - Perl 6). If it is recommended to stick with version 2, should I use the latest (2.6.4 or 2.7), and if so why? Thanks. The latest stable one, 2.6.4 (2.7 is a preview release); there's no reason not to, and newer versions have more features, bugfixes, etc. Though you should double-check the compatibility of any libraries you'll be using of course. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Is python not good enough?
On Wed, Jan 13, 2010 at 1:06 AM, tanix ta...@mongo.net wrote: In article 53ec94c0-dbdd-4901-a46b-d7faee121...@j14g2000yqm.googlegroups.com, johan.san...@gmail.com johan.san...@gmail.com wrote: On Jan 13, 12:55=A0am, a...@pythoncraft.com (Aahz) wrote: In article 1b42700d-139a-4653-8669-d4ee2fc48...@r5g2000yqb.googlegroups.= com, ikuta liu =A0ikut...@gmail.com wrote: Is python not good enough? for google, enhance python performance is the good way better then choose build Go language? It is not at all clear that -- despite some comments to the contrary -- the Go developers are intending to compete with Python. =A0Go seems much more intended to compete with C++/Java. =A0If they're successful, we may eventually see GoPython. =A0;-) -- Aahz (a...@pythoncraft.com) =A0 =A0 =A0 =A0 =A0 * =A0 =A0 =A0 =A0http:/= /www.pythoncraft.com/ If you think it's expensive to hire a professional to do the job, wait until you hire an amateur. =A0--Red Adair GoPython i think would be neat. Well, as soon as they restore the braces to identify the code blocks and provide the functionality of advanced statically type languages, such as threads, async processing, all synchronization primitives, garbage collection, events and GUI, i'd be willing to switch to Python. Some of it is already there. But not all. Except, before doing it, I'd like to know what Python buys me compared to say Java. The lack of knowledge shown here gives me even less confidence in your Goldmine collections than before. Cheers, Chris -- http://blog.rebertia.com -- Programmer's Goldmine collections: http://preciseinfo.org Tens of thousands of code examples and expert discussions on C++, MFC, VC, ATL, STL, templates, Java, Python, Javascript, PHP, organized by major topics of language, tools, methods, techniques. -- http://mail.python.org/mailman/listinfo/python-list
Re: Sort list of dictionaries by key (case insensitive)
On Tue, Jan 12, 2010 at 11:45 PM, Nico Grubert nicogrub...@gmail.com wrote:
Hi there
I have the following list 'mylist' that contains some dictionaries:
mylist = [{'title':'the Fog', 'id':1},
{'title':'The Storm', 'id':2},
{'title':'the bible', 'id':3},
{'title':'The thunder', 'id':4}
]
mylist.sort(key = lambda d: d['title'])
Use operator.itemgetter() to optimize in the unlikely event it becomes
necessary.
Cheers,
Chris
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