Mailman 3 April 2010 - Python-ideas

Reversable
by cool-RR April 29, 2010

April 29, 2010

Just something small that I thought of, and I haven't thought about this deeply at all, so maybe this is way wrong. But: What about adding a `Reversable` next to all the `Iterable` and `Container` and stuff? (Please `cc` any replies to me, I'm not getting mail from this list.) Ram.

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math.fsum: summing multiple running sums at once
by Ilya Shlyakhter April 29, 2010

April 29, 2010

A suggestion: extend math.fsum to accept an iterable that yields tuples of floats, and returns a tuple of sums. This would permit summing multiple running sums at once (e.g. keeping both a sum and a sum-of-squares for computing standard deviation from an iterable), or summing a stream of complex numbers. An alternative would be to make an object-oriented version of fsum that has a method for adding a number to the sum; then an array of such objects could be used to sum multiple iterables … [View More]

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why has itertools.imap other semantics as the bultin map?
by Mathias Panzenböck April 29, 2010

April 29, 2010

See: >>> map(None,['a','b'],[]) [('a', None), ('b', None)] >>> list(imap(None,['a','b'],[])) [] Why is that? I propose that imap should work like map (except from being a generator, of course). System Info: Python 2.6.2 (r262:71600, Jan 25 2010, 18:46:47) [GCC 4.4.2 20091222 (Red Hat 4.4.2-20)] on linux2 -panzi

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Why no sign function?
by cool-RR April 27, 2010

April 27, 2010

This was probably discussed a lot. Why is there no simple `sign` function in Python, like in the math module or something? I mean one that tells you the sign of a number. Ram.

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Re: [Python-ideas] Anaphoric if
by Jess Austin April 26, 2010

April 26, 2010

On Fri, Apr 23, 2010 at 3:47 PM, Andrey Fedorov <anfedorov(a)gmail.com> wrote: > I imagine this has been covered before, but somehow my Google-foo is > failing. What are people's opinions about having an anaphoric-if syntax > sugar like: > > if foo() as x: > ... x > > > meaning > > x = foo() > if x: > ... x > I like this, and I'd like for it to be in python, although I don't think it will be widely supported because it … [View More]

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Anaphoric if
by Andrey Fedorov April 24, 2010

April 24, 2010

I imagine this has been covered before, but somehow my Google-foo is failing. What are people's opinions about having an anaphoric-if syntax sugar like: if foo() as x: ... x meaning x = foo() if x: ... x ? I do this a lot, and it seems very un-Pythonically verbose to repeat "x" (especially when a longer variable name is appropriate). Cheers, Andrey

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Re: [Python-ideas] Anaphoric if
by Bruce Leban April 23, 2010

April 23, 2010

def anaphor(x): return (x,) if x else () for foo in anaphor(bar): ... --- Bruce (via android) On Apr 23, 2010 4:18 PM, "Chris Rebert" <pyideas(a)rebertia.com> wrote: On Fri, Apr 23, 2010 at 1:47 PM, Andrey Fedorov <anfedorov(a)gmail.com> wrote: > I imagine this has be... Master Yoda had me google "python-ideas if assignment", which was fruitful: [Python-ideas] Inline assignment expression: http://mail.python.org/pipermail/python-ideas/2009-March/003423.html Post in … [View More]

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Re: [Python-ideas] Small enhancement to os.path.splitext
by Bruce Leban April 23, 2010

April 23, 2010

Also note that there are really THREE variations: Case sensitive (Unix/mac normally) Case preserving (windows normally) Case insensitive (some legacy fs) IMHO gcc treating .c and .C is annoying. I usually get .JPG instead of .jpg when windows apps pick the extension for me. Also annoying. Notwithstanding that you can't do case insensitive compare without knowing the file system locale otherwise .GIF != .gif. So this is a mess. Furthermore it's not just extensions. Some names are … [View More]

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Re: [Python-ideas] Small enhancement to os.path.splitext
by Paul Moore April 23, 2010

April 23, 2010

Sorry, should have gone to the list. On 23 April 2010 01:53, Greg Ewing <greg.ewing(a)canterbury.ac.nz> wrote: > I still don't think you can decide based on the file > system behaviour. What if the user creates his files on > a case-insensitive system and then copies them to a > case-sensitive one or vice versa? The intended meaning > of the extensions doesn't suddenly change when that > happens. I don't know if you actually use case insensitive filenames regularly (an … [View More]odd question that, in "normal life" I'd immediately assume 99.99% of people I meet use Windows, but on this list, I tend to assume most people use Unix/Linux or Mac - sorry if my assumption's mistaken) but personally, as a Windows user, I try to keep filename case the way I want it, but I'd tend to double check if moving files to a case sensitive system. But - and this is the key point here for me - the filenames I *type* at the command line often don't match the case on the filesystem (because I'm too lazy to hit the shift key when I know it doesn't matter, for example) and so my expectations very much are based on filesystem case sensitivity, and what's more, it's what I type that's unreliable. As far as I am concerned, any behaviour that relies on filenames differing only in case being handled differently is wrong on Windows. (Yes, that includes gcc's behaviour). All programs should work case insensitively in all cases when dealing with files. Simple. That's my view as a Windows user. I rationalise it as being based on the case sensitivity of the filesystem, but I'll admit I have no experience with using case sensitive filesystems on Windows (for all practical purposes, they don't exist). I also have limited experience with Unix, and all my Unix experience is in situations where all the filesystems are case sensitive. So arguably, my position is Unix == case sensitive, Windows = case insensitive, and a simple switch on sys.platform would work for me. But desktop Linux systems need to deal with such things as FAT32-formatted USB disks, Samba filesystems, etc. And I have no good intuition on how they should be handled. So I fall back on my original rationalisation, that the filesystem behaviour is what matters. So to summarise: * Case sensitivity behaviour determined by host OS would work for me * But it "feels" wrong * Case sensitive everywhere is completely wrong (as it ignores Windows users' expectations) * Choosing a default based on filesystem behaviour is logical, but hard, and there may be no real requirement for it Also, making the user choose every time (for example, GNU find with its -name and -iname options) is not a helpful or portable approach (e.g., I want find . -name *.sql to find all SQL scripts, regardless of platform). Cross-platform tools with a strong focus on file and filename semantics (for example, DVCSs such as Mercurial) have specialist needs, and probably should always write custom code. But for "quick" scripts, something in the standard library which made doing the "right" thing easy would be a huge help. Paul [View Less]

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Re: [Python-ideas] Small enhancement to os.path.splitext
by Bruce Leban April 23, 2010

April 23, 2010

When would you know in advance you want 2 parts? Compare file.tar.gz to backup.2010.04.20.tar. I'd think the usual case would be split if gz or zip or...: split again --- Bruce (via android) On Apr 20, 2010 8:36 AM, "Tarek Ziadé" <ziade.tarek(a)gmail.com> wrote: Hello Currently, os.path.splitext will split a string giving you the piece behind the last dot: >>> os.path.splitext('file.tar.gz') ('file.tar', '.gz') In some cases, what we really want is the two last parts … [View More]

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Small suggestion re help(Exception)
by Rob Cliffe April 21, 2010

April 21, 2010

help() on an Exception class lists the method resolution order (effectively the inheritance hierarchy). E.g. help(ArithmeticError) displays inter alia: Method resolution order: ArithmeticError StandardError Exception BaseException __builtin__.object Would it be possible for it also display the Python built-in SUBclasses of the class? E.g. in the same example something like: Built-in subclasses: FloatingPointError OverflowError ZeroDivisionError This may seem … [View More]

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Re: [Python-ideas] [PyQt] Carol Newman
by Chris Kaynor April 20, 2010

April 20, 2010

There was a G-mail invasion earlier today that allowed e-mails to be sent from any g-mail account without the owner's permission. Chris On Tue, Apr 20, 2010 at 3:06 PM, Nick Gaens <mail(a)nickgaens.com> wrote: > Please someone remove this address from the lists, because of spamming.. > > > -- > Nick Gaens > > -- > http://mail.python.org/mailman/listinfo/python-list > >

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Carol Newman
by Zac Burns April 20, 2010

April 20, 2010

http://www.ristorantealpirata.com/home.php -- Zachary Burns (407)590-4814 Aim - Zac256FL Production Engineer Zindagi Games

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__decorate__ method
by Zac Burns April 20, 2010

April 20, 2010

I would like to propose an extension to behavior the decorator syntax. For @decorator '@' should see if decorator supplies a __decorate__ method. If so, call the __decorate__ method. Otherwise, call decorator directly. Guido does say that __decorate__ should not replace __call__ here http://markmail.org/message/ig6diu6j55flxr6c, saying """ Q: Is there a strong feeling (in any direction) about calling the decorator's "decorate" or "__decorate__" attribute, rather than its "__call__" attribute? … [View More]

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Small enhancement to os.path.splitext
by Tarek Ziadé April 20, 2010

April 20, 2010

Hello Currently, os.path.splitext will split a string giving you the piece behind the last dot: >>> os.path.splitext('file.tar.gz') ('file.tar', '.gz') In some cases, what we really want is the two last parts when splitting on the dots (like in my example). What about providing an extra argument to be able to grab more than one dot ? >>> os.path.splitext('file.tar.gz', numext=2) ('file', '.tar.gz') If numext > numbers of dots, it will just split after the first dot: … [View More]

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@return?
by Conrad Irwin April 18, 2010

April 18, 2010

Dear All, I have an idea, though the acceptability of it is a matter for debate. It seems that this would be the appropriate place to post, but if not, or if you've already tired of this proposal, sorry. A common pattern when creating decorators is something of the form: def decorator(func): def wrapper(*args): func(modulate(args)) return wrapper This is surprisingly reminiscent of the kind of code decorators were introduced to avoid: class Example(… [View More]

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"value" ~ "data" ~ "object"
by spir ☣ April 17, 2010

April 17, 2010

Hello, I have been recently thinking at lexical distinctions around the notion of data. (--> eg for a starting point http://c2.com/cgi/wiki?WhatIsData) Not only but especially in Python. I ended up with the following questions: Can one state "in Python value=data=object"? Can one state "in Python speak value=data=object"? What useful distinctions are or may be done, for instance in documentation? What kind of difference in actual language semantics may such distinctions mirror? Denis PS: … [View More]

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Fwd: Re: @return?
by Conrad Irwin April 16, 2010

April 16, 2010

On 04/16/2010 03:52 AM, alex23 wrote: > Conrad Irwin <conrad.ir...(a)googlemail.com> wrote: >> result = register_callback(def success(arg): >> print(arg) >> ) >> >> I think it is significantly nicer than the decorator abuse: >> >> @register_callback >> def result(arg): >> print(arg) > > How is that an abuse of the decorator syntax? Well, It … [View More]would be clearer expanded as: def success(arg): print(arg) result = register_callback(success) But in order to assign the result to "result", I renamed the function, register_callback returns an int. > > How is your @return syntax more clear in its intent than: > > from decorator import decorator > > @decorator > def a_decorator(...): > .... @decorator solves one common case extremely well, though perusing its documentation I notice lots of "@return" use still - in any decorator that takes parameters before the function (arguably this could be solved by modifying "@decorator"). I also feel that, in the memoize example, the author has gone out of his way to use @decorator where creating an enclosing scope and "@return"ing would be less intrusive. > Is returning a function from within another function - outside of > decorators - that recurring a task that we need new syntax that not > only overloads existing syntax for a different use, but also disrupts > the readability of a function? In light of the above, yes, there are enough uses for it, and the feeling of cleanliness it provides. Using it with classes is also useful (found in django) - though much rarer: def infix(bp, func): class Operator(TokenBase): ... def led(self, left, parser): ... def eval(self, context): ... return Operator The syntax overloading was intentional, "@return" is very like a decorator in behaviour (albeit not in implementation). Introducing a new syntax to do something so similar seems very heavy-handed. Having @return next to the definition emphasizes that flow of control, and (particularly for lengthy definitions) doesn't leave an orphaned return statement floating somewhere at the end. def infix(bp, func): @return class Operator(TokenBase): ... def led(self, left, parser): ... def eval(self, context): ... Obviously, on matters of aesthetics, anyone can be right. I am, however, convinced that avoiding repetition (even if it is just of a name) in an unambiguous manner is a worthy goal. Conrad [View Less]

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question - 'bag' type
by C. Titus Brown April 15, 2010

April 15, 2010

Hi all, this seems like the right forum to ask -- is there a reason why Python doesn't have a 'bag' builtin type, e.g. b = bag(foo=bar, baz=bif) assert b.foo == bar assert b.bz == bif ? It's easy to write and there's a great discussion over at the cookbook: http://code.activestate.com/recipes/259174-bag-collection-class/ Inquiring minds want to know! thanks, --titus -- C. Titus Brown, ctb(a)msu.edu

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Re: [Python-ideas] CSV api with conversion
by Bruce Leban April 15, 2010

April 15, 2010

Sure I could do that. I just this think if you're making a convenience function like this you should strive to make it more convenient. :-) --- Bruce (via android) On Apr 14, 2010 4:03 PM, "MRAB" <python(a)mrabarnett.plus.com> wrote: Bruce Leban wrote: > > If you do this, you'll probably want to support mapping empty values. That is... The actual values read from the CSV file are strings and you're passing them to functions: int("1"), str("") int(""), str("2") If you … [View More]

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CSV api with conversion
by Denis Kolodin April 14, 2010

April 14, 2010

Hello! My name is Denis Kolodin. I live in Russia, Tambov. I was developing much time with C, Java, C#, R. But two month ago I'm using Python. It's really cool. Now, I move ALL my projects to it fully and have some ideas which API's extensions may will be useful. The first thing I want to say about is an extension of CSV api. In R language I could to set types for the every column in a csv file. I propose to add a same function to the Python's standard library. Here it is (Python 3 version): … [View More]

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max() allowed to take empty list
by Tom Pinckney April 13, 2010

April 13, 2010

Many functions are happy to take empty lists: >>> map(lambda x: x, []) [] >>> filter(lambda x: x == 1, []) [] >>> sum(a) 0 >>> reduce(lambda x,y: x+y, [], 0) 0 But not max(): >>> max([]) Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: max() arg is an empty sequence Allowing max to return None would make a lot of functional style programming easier, instead of explicitly having to check for empty … [View More]

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Testcase.assertsequenceequal() suggestion
by Floris Bruynooghe April 8, 2010

April 8, 2010

Hi I've found myself modifying the unittest.TestCase.assertSequenceEqual() method to suppress the diff of the two sequences if the diff is more then a few lines and was wondering if this was something worth considering in the stdlib in some form or another. The resulting message still contains useful information since it still prints the first differing elements, and it avoids flooding the screen with lots of data for long sequences. Regards Floris -- Debian GNU/Linux -- The Power of … [View More]

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The 'instruction' event of python debugger
by Ray Allen April 6, 2010

April 6, 2010

Hi, all: I've been studying into python for a time. When I'm using the python debugger, I found for the python code run step, the smallest granularity is one single python source line(corresponding to the 'line' event in the debugger implementation), that means we can stop at every python source line and do something, for example, print an object, watch the stack, and so on. Sometimes I feel it's not small enough, I need another trace event: instruction. This event occurs at every … [View More]

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Re: [Python-ideas] [Python-Dev] Scope object (Re: nonlocals() function?)
by Greg Ewing April 6, 2010

April 6, 2010

Antoine Pitrou wrote: > It is useful to distinguish between globals (i.e., module-level variables) and > locals, so replacing them with scope() would not be better IMO. You have a point about globals(), so it probably makes sense for it to stay. I still think that it wouldn't hurt to subsume locals() and the proposed nonlocals() into a single function returning some kind of view object, though. But I suppose we'd have to examine use cases before deciding that. The main use case I can … [View More]

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