🌐 Mailman 3 July 2008 - Python-list - python.org

Standard module for parsing emails?
by Phillip B Oldham July 31, 2008

July 31, 2008

Is there a standard library for parsing emails that can cope with the different way email clients quote?

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Re: Python parsing iTunes XML/COM
by william tanksley July 31, 2008

July 31, 2008

"Jerry Hill" <malaclyp...(a)gmail.com> wrote: > On Wed, Jul 30, 2008 at 2:27 PM, william tanksley <wtanksle...(a)gmail.com> wrote: > > Awesome... Thank you! I had my mental model of Python turned around > > backwards. That's an odd feeling. Okay, so you decode to go from raw > > byes into a given encoding, and you encode to go from a given encoding > > to raw bytes. Not what I thought it was, but that's cool, makes sense. > That's not quite right. Decoding takes a byte string that is already > in a particular encoding and transforms it to unicode. Unicode isn't > a encoding of it's own. Decoding takes a unicode string (which > doesn't have any encoding associated with it), and gives you back a > sequence of bytes in a particular encoding. Okay, this is useful. Thank you for straightening out my mental model. It makes sense to define strings as just naturally Unicode... and anything else is in some ways not really a string, although it's something that might have many of the same methods. I guess this mental model is being implemented more thoroughly in Py3K... Anyhow, it makes sense. I'm still puzzled why I'm getting some non-Unicode out of an ElementTree's text, though. > Jerry -Wm

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Case tagging and python
by Fred Mangusta July 31, 2008

July 31, 2008

Hi, I'm relatively new to programming in general, and totally new to python, and I've been told that this language is particularly good for what I need to do. Let me explain. I have a large corpus of English text, in the form of several files. First of all I would like to scan each file. Then, for each word I find, I'd like to examine its case status, and write the (lower case) word back to another text file - with, appended, a tag stating the case it had in the original file. An example. Suppose we have three possible "case conditions" -all lowercase -all uppercase -initial uppercase only Three corresponding tags for each of these might be, respectively: -nocap -allcaps -cap Therefore, given the string "The Chairman of BP was asleep" I would like to produce "the/cap chairman/cap of/nocap /bp/allcaps was/nocap /asleep/nocap" and writing this into a file. I have the following algorithm in mind: -open input file -open output file -get line of text -split line into words -for each word -tag = checkCase(word) -newword = lowercase(word) + append(tag) rejoin words into line write line into output file Now, I managed to write the following initial code for s in file: lines += 1 if lines % 1000 == 0: print '%d lines' % We print the total lines sent = s.split() #split string by spaces #... But then I don't quite know what would be the fastest/best way to do this. Could I use the join function to reform the string? And, regarding the casetest() function, what do you suggest to do? Should I test each character of each word or there are faster methods? Thanks very much, F.

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Re: simple problem with lists I am just forgetting
by bearophileHUGS＠lycos.com July 31, 2008

July 31, 2008

Alexnb: > How can I test if the list item is empty without getting that exception? In Python such list cell isn't empty, it's absent. So you can use len(somelist) to see how much long the list is before accessing its items. Often you can iterate on the list with a for, so you don't need to care of the len(). Bye, bearophile

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simple problem with lists I am just forgetting
by Alexnb July 31, 2008

July 31, 2008

Lets say we have this list: funlist = ['a', 'b', 'c'] and lets say I do this: if funlist[4]: print funlist[4] I will get the exception "list index out of range" How can I test if the list item is empty without getting that exception? -- View this message in context: http://www.nabble.com/simple-problem-with-lists-I-am-just-forgetting-tp1876… Sent from the Python - python-list mailing list archive at Nabble.com.

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Re: Boolean tests [was Re: Attack a sacred Python Cow]
by Steven D'Aprano July 31, 2008

July 31, 2008

On Wed, 30 Jul 2008 09:23:05 -0600, Matthew Fitzgibbons wrote: > If you're expecting a list (and only a list) > then your point makes sense. 'if x' can get you into trouble if you > _don't_ want its polymorphism. "if x" is hardly unique in that way. If you're expecting a list, and only a list, "len(x) != 0" will get you in trouble if somebody passes a string or a dictionary. I don't see any reason why we should single out "if x" as dangerous in the face of invalid types. With the exception of the "is" and "is not" operators, nothing in Python is guaranteed to work with any imaginable object. Even print can fail, if the object's __str__ method raises an exception. > Although, if my function is expecting a list, my preference is to do: > > if not isinstance(x, list): > raise SomeMeaningfulException() > # do stuff with the list > > I put my type checking at the top of the function, so readers can > reference it easily. And thus you break duck-typing and upset anybody who wants to pass a sequence that doesn't inherit directly from list. There are other (and arguably better, although more labour-intensive) techniques for defensive programming that don't break duck-typing. You can google for Look Before You Leap and Easier To Ask Forgiveness Than Permission for more information. Alex Martelli has a fine recipe in the Python Cookbook -- search for the recipe "Checking if an object has the necessary attributes". But in a nutshell, here's a toy example: def spam(seq): try: seq.append seq.extend seq[0] = seq[0] except Exception: raise TypeError("argument isn't sufficiently sequence-like") # No exceptions expected from here on seq.append(seq[0]) seq.extend([1,2,3]) seq[0] = "spam" -- Steven

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Re: Attack a sacred Python Cow
by Carl Banks July 31, 2008

July 31, 2008

On Jul 26, 5:07 pm, Terry Reedy <tjre...(a)udel.edu> wrote: > Whether or not one should write 'if x' or 'if x != 0' [typo corrected] > depends on whether one means the general 'if x is any non-null object > for which bool(x) == True' or the specific 'if x is anything other than > numeric zero'. The two are not equivalent. Ditto for the length example. Can you think of any use cases for the former? And I mean something where it can't be boiled down to a simple explicit test for the sorts of arguments you're expecting; something that really takes advantage of the "all objects are either true or false" paradigm. The best thing I can come up with out of my mind is cases where you want to check for zero or an empty sequence, and you want to accept None as an alternative negative as well. But that's pretty weak. The use case of simply passing something to a function that accepts any boolean doesn't count. For instance, I could write: def nand(a,b): return not (a and b) And then I could use it like this, even if x is an interger and y a string: if nand(x,y): But that doesn't buy much since I could just pass in the explicit tests like this: if nand(x!=0,y!=""): Carl Banks

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Re: problem when reading file
by Bruce Frederiksen July 31, 2008

July 31, 2008

On Thu, 31 Jul 2008 23:44:33 +1000, shrimpy wrote: > hi every one, i am new to python, > and coz i want to write a handy command for my linux machine, to find > a word in all the files which are under the current folder. > > the code is half done, but when i run it, it complain, and i don`t know why??? > > can anyone help me have a look at it? > > > here is the message it complain > ======================================= > file is : qt_plugins_3.3rc > > Traceback (most recent call last): > File "./python_script/svn_grep.py", line 34, in <module> > searPatten(file,'are','no') > File "./python_script/svn_grep.py", line 8, in searPatten > openFile = open(file, 'r') > IOError: [Errno 2] No such file or directory: 'qt_plugins_3.3rc' > > > here are the code i wrote > ---------------------------------------------------------------code begin > <snip> > > for root, dirs, files in os.walk(os.getcwd()): > for file in files: > print "=======================================" > print "file is : " + file + "\n" > searPatten(file,'are','no') > > ---------------------------------------------------------------code end Try changing that last line to: searPatten(os.path.join(root, file), 'are', 'no') You'll have to import os.path too...

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Re: Difference between type and class
by Nikolaus Rath July 31, 2008

July 31, 2008

Maric Michaud <maric(a)aristote.info> writes: > Le Thursday 31 July 2008 14:30:19 Nikolaus Rath, vous avez écrit : >> oj <ojeeves(a)gmail.com> writes: >> > On Jul 31, 11:37 am, Nikolaus Rath <Nikol...(a)rath.org> wrote: >> >> So why does Python distinguish between e.g. the type 'int' and the >> >> class 'myclass'? Why can't I say that 'int' is a class and 'myclass' >> >> is a type? >> > >> > I might be wrong here, but I think the point is that there is no >> > distinction. A class (lets call it SomeClass for this example) is an >> > object of type 'type', and an instance of a class is an object of type >> > 'SomeClass'. >> >> But there seems to be a distinction: >> >>> class int_class(object): >> >> ... pass >> ... >> >> >>> int_class >> >> <class '__main__.int_class'> >> >> >>> int >> >> <type 'int'> >> >> why doesn't this print >> >> >>> class int_class(object): >> >> ... pass >> ... >> >> >>> int_class >> >> <type '__main__.int_class'> >> >> >>> int >> >> <type 'int'> >> >> or >> >> >>> class int_class(object): >> >> ... pass >> ... >> >> >>> int_class >> >> <class '__main__.int_class'> >> >> >>> int >> >> <class 'int'> >> >> If there is no distinction, how does the Python interpreter know when >> to print 'class' and when to print 'type'? >> > > There are some confusion about the terms here. > > Classes are instances of type 'type', Could you please clarify what you mean with 'instance of type X'? I guess you mean that 'y is an instance of type X' iif y is constructed by instantiating X. Is that correct? > What the <type int> means is that int is not a user type but a > builtin type, instances of int are not types (or classes) but common > objects, so its nature is the same as any classes. > > The way it prints doesn't matter, it's just the __repr__ of any instance, and > the default behavior for instances of type is to return '<class XX>', but it > can be easily customized. But 'int' is an instance of 'type' (the metaclass): >>> int.__class__ <type 'type'> so it should also return '<class int>' if that's the default behavior of the 'type' metaclass. I think that to get '<type int>' one would have to define a new metaclass like this: def type_meta(type): def __repr__(self) return "<type %s>" % self.__name__ and then one should have int.__class__ == type_meta. But obviously that's not the case. Why? Moreover: >>> class myint(int): ... pass ... >>> myint.__class__ == int.__class__ True >>> int <type 'int'> >>> myint <class '__main__.myint'> despite int and myint having the same metaclass. So if the representation is really defined in the 'type' metaclass, then type.__repr__ has to make some kind of distinction between int and myint, so they cannot be on absolute equal footing. Best, -Nikolaus -- »It is not worth an intelligent man's time to be in the majority. By definition, there are already enough people to do that.« -J.H. Hardy PGP fingerprint: 5B93 61F8 4EA2 E279 ABF6 02CF A9AD B7F8 AE4E 425C

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Re: undo a dictionary
by mmm July 31, 2008

July 31, 2008

Gabriel, I meant the latter, so this helps > Or, do you mean you already have those names and values, perhaps mixed > with a lot more names, and want to extract only those starting with "x" > and following with a number? > > result = {} > for name, value in vars(): # or locals().items(), or globals().items(), or > vars(some_module) > if name[0]=='x' and name[1:].isdigit(): > result[name] = value But I got an error with 'for name, value in vars():' RuntimeError: dictionary changed size during iteration I think globals() has the same problem, but globals.items() works. I will need to read the docs to learn why '.items()' works but the changing global dictionary problem makes sense. I assume I need to use a non dynamic created list. Sometimes I get the error about 'too many variables to unpack' (can not consistently repeat the error however) In any event, thanks for the suggestions, everyone. Using a blank class for unpacking the dictionary makes the most sense, for safety sake. So you know the general issue is I want to switch between using dictionaries for storing data items and simple variable names for writing equations/formulas, So (a) and (b) below are preferred to (c) for readability (a) straight forward equation y = b0 + b1*Age + b2*Size (b) Class version y = b0 + b1*x.Age + b2*x.Size (c) Dictionary version y = b0 + b1*dd.get('Age') + b2*dd.get('Size')

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