🌐 Mailman 3 August 2007 - Python-list - python.org

Determining if file is valid image file
by André Aug. 2, 2007

Aug. 2, 2007

Other than installing PIL, is there a "simple" way using Python only to determine if a file is a valid image file? I'd be happy if I could at least identify valid images files for gif, jpeg and png. Pointers to existing modules or examples would be appreciated. The reason why I'd prefer not using PIL is that I'd like to bundle such a function/module in my app. André

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Catching SystemExit in C API code when embedding Python?
by Stefan Bellon Aug. 2, 2007

Aug. 2, 2007

Hi all! I am embedding Python into a GUI application in a way that the GUI is scriptable using Python. Now I have come to a problem that when the user puts a "sys.exit(0)" into his script to end the script, not only the script is terminated, but also the GUI application itself. This is not the intended behaviour. As in Python itself you can catch SystemExit, I think this should be the way to go. But how do I catch this exception from within the C API? Thanks in advance for any hints. -- Stefan Bellon

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Re: Error subclassing datetime.date and pickling
by kyosohma＠gmail.com Aug. 2, 2007

Aug. 2, 2007

On Aug 2, 11:02 am, Mike Rooney <m...(a)qvii.com> wrote: > Hi everyone, this is my first post to this list. I am trying to create a > subclass of datetime.date and pickle it, but I get errors on loading it > back. I have created a VERY simple demo of this: > > import datetime > > class MyDate(datetime.date): > """ > This should be pickleable. > > >>> md = MyDate(2007, 1, 6) > >>> import pickle > >>> pickle.dump(md, open("test.pickle", 'w')) > >>> mdp = pickle.load(open("test.pickle")) > >>> import os; os.remove("test.pickle") > """ > def __init__(self, y, m, d): > datetime.date.__init__(self, y, m, d) > > if __name__ == "__main__": > import doctest > doctest.testmod() > > The traceback that occurs is: > > Traceback (most recent call last): > File "C:\Python25\lib\doctest.py", line 1212, in __run > compileflags, 1) in test.globs > File "<doctest __main__.MyDate[3]>", line 1, in <module> > mdp = pickle.load(open("test.pickle")) > File "C:\Python25\lib\pickle.py", line 1370, in load > return Unpickler(file).load() > File "C:\Python25\lib\pickle.py", line 858, in load > dispatch[key](self) > File "C:\Python25\lib\pickle.py", line 1133, in load_red > value = func(*args) > TypeError: __init__() takes exactly 4 arguments (2 given) > > I have found a few relating issues: > -https://sourceforge.net/tracker/?func=detail&atid=105470&aid=952807&g... > -http://sourceforge.net/tracker/index.php?func=detail&aid=720908&group... > > But these are both rather old and are marked as fixed. I am running > Python 2.5.1 on Windows XP SP2. Any help here would be greatly appreciated! > > - Mike I've never used pickle or shelve in my applications...yet. I tried separating out the class into its own module and importing it, as pickling classes is supposed to be tricky. I looked through all my Python books and what few examples I found looked just like your code. I did find this article which might be helpful to you more than it was to me: http://www.ibm.com/developerworks/library/l-pypers.html >From what I can tell, when your object gets unpickled it only passes 2 arguments to the class instead of the 4 that were supposed to be pickled. If you change the number of arguments that the class accepts and re-pickle it, you'll see that the unpickle object traceback corresponds. It's very weird. Sorry I didn't have some slam-bang awesome idea. Mike

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Re: problems playing with dates from any month.
by kyosohma＠gmail.com Aug. 2, 2007

Aug. 2, 2007

On Aug 2, 1:16 pm, "krishnakant Mane" <researchb...(a)gmail.com> wrote: > On 02/08/07, Ian Clark <icl...(a)mail.ewu.edu> wrote: > > > > >http://docs.python.org/lib/node85.html > > I looked there even before. > but could not figure out what the code did. > I know in that variable called s there was a string in a valid date format. > but when datetime.strptime was used, I did not understand the place > where a date object say d was created. > I would expect some thing like d = and the function. but I did not fine that. > only reference was the datetime module and the documentation is not as good. > another question I am getting is that where is the list of all > formatting characters. like for example Y is 4 digit year M is month > MM is month in 2 digits etc. > I am trying to locate a list of all these denoters. > can you provide me the place? > > > Then it's just: > > > if date_obj.day == 5: > > print 'It's the fifth day of the month' > > this was much better than the documentation, thanks, > regards, > Krishnakant. The various flags for the strftime() are here, near the middle of the page: http://docs.python.org/lib/module-time.html Not sure why the docs don't point to this page when talking about the datetime's almost identical method. Mike

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Re: __call__ considered harmful or indispensable?
by Diez B. Roggisch Aug. 2, 2007

Aug. 2, 2007

skip(a)pobox.com schrieb: > I don't personally use __call__ methods in my classes, but I have > encountered it every now and then here at work in code written by other > people. The other day I replaced __call__ with a more obvious method name, > so now instead of executing > > obj(foo, bar, baz) > > the code in question is > > obj.execute(foo, bar, baz) > > In this case there was a bug. Depending on inputs, sometimes obj > initialized to a class, sometimes an instance of that class. (I fixed that > too while I was at it.) The problem was that the use of __call__ obscured > the underlying bug by making the instance as well as the class callable. > > In this particular case it was clearly unnecessary and just obfuscated the > code. I'm wondering, are there some general cases where __call__ methods of > a user-defined class are simply indispensable? Thanks to closures and bound methods, I don't think that there is a case where you can't "fake" the missing __call__ at least when it comes to call-backs. So in the end, you can always work around that. But if you don't need to... Se the gnosis multimethods for an implementation that makes sensible use of the __call__-operator in my opinion. diez

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XML Processing
by Roman Aug. 2, 2007

Aug. 2, 2007

Is there a package that converts a string that contains special characters in xml to to literal value. For instance, converts string http://myhome/&param to http://myhome/&param. Thanks in advance

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Re: __call__ considered harmful or indispensable?
by Neil Cerutti Aug. 2, 2007

Aug. 2, 2007

On 2007-08-02, skip(a)pobox.com <skip(a)pobox.com> wrote: > I don't personally use __call__ methods in my classes, but I > have encountered it every now and then here at work in code > written by other people. The other day I replaced __call__ > with a more obvious method name, so now instead of executing > > obj(foo, bar, baz) > > the code in question is > > obj.execute(foo, bar, baz) > > In this case there was a bug. Depending on inputs, sometimes > obj initialized to a class, sometimes an instance of that > class. (I fixed that too while I was at it.) The problem was > that the use of __call__ obscured the underlying bug by making > the instance as well as the class callable. > > In this particular case it was clearly unnecessary and just > obfuscated the code. I'm wondering, are there some general > cases where __call__ methods of a user-defined class are simply > indispensable? In C++ they are called functors, and they are very useful as surrogate functions with state. I haven't seen them used in the same way in Python much, because Python has more immediate solutions to (most of) these problems. Here's a (somewhat goofy) example: class is_consecutive(object): def __init__(self, seed, compare=operator.lt): self.last_value = seed self.compare = compare def __call__(self, total, value): if total is False: return False lv = self.last_value self.last_value = value return self.compare(lv, value): a = range(15) >>> reduce(is_consecutive(0), a) True >>> reduce(is_consecutive(0), a + [1,2]) False It's been a while since I had to be in the STL mindset, so I couldn't think of a better example. -- Neil Cerutti This is not a book to be put down lightly. It should be thrown with great force. --Dorothy Parker

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problems playing with dates from any month.
by krishnakant Mane Aug. 2, 2007

Aug. 2, 2007

hello, I have a very strange problem and I can't find any solution for that. I am working on an accounting package which I wish to develop in python. the simple problem is that I want to knoe how I can know if the given date is the nth day of a month. for example if a customer is supposed to pay his installment on every 5th of all months, I want to know if today is the fifth day (jan the fifth, feb the fifth etc) for any given month. I have not found any such function. if I have looked (or over looked ) in the wrong places I am really sorry. secondly I also want to know the way in which I can convert a given string to a date object. for example if I have a string "29/09/2005", I know it is a valid date although it is in a string form. now I want to convert the above string into a real date object. how can I cast it this way? regards, Krishnakant.

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Re: problems playing with dates from any month.
by kyosohma＠gmail.com Aug. 2, 2007

Aug. 2, 2007

On Aug 2, 12:31 pm, "krishnakant Mane" <researchb...(a)gmail.com> wrote: > hello, > I have a very strange problem and I can't find any solution for that. > I am working on an accounting package which I wish to develop in python. > the simple problem is that I want to knoe how I can know if the given > date is the nth day of a month. > for example if a customer is supposed to pay his installment on every > 5th of all months, > I want to know if today is the fifth day (jan the fifth, feb the fifth > etc) for any given month. > I have not found any such function. > if I have looked (or over looked ) in the wrong places I am really sorry. > secondly I also want to know the way in which I can convert a given > string to a date object. > for example if I have a string "29/09/2005", I know it is a valid date > although it is in a string form. > now I want to convert the above string into a real date object. > how can I cast it this way? > regards, > Krishnakant. You should also check this place out: http://labix.org/python-dateutil Lots of cool date manipulation using the dateutil module. Mike

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Re: Emacs + python
by hg Aug. 2, 2007

Aug. 2, 2007

Edward O'Connor wrote: >> Could anyone put me on the right track to developing Python with emacs >> please : modes to consider, debugging etc hopefully all within emacs. > > Personally, I prefer the python.el that ships with Emacs 22 to the > python-mode.el from python.org. It seems more like other Emacs major > modes. > > > Ted > > -- > Edward O'Connor > hober0(a)gmail.com > > Ense petit placidam sub libertate quietem. Are there any cscope & ECB equivalent for Python ? Thanks hg

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