Mailman 3 December 2013 - Python-ideas

@classproperty, @abc.abstractclasspropery, etc.
by K. Richard Pixley Dec. 16, 2020

Dec. 16, 2020

There's a whole matrix of these and I'm wondering why the matrix is currently sparse rather than implementing them all. Or rather, why we can't stack them as: class foo(object): @classmethod @property def bar(cls, ...): ... Essentially the permutation are, I think: {'unadorned'|abc.abstract}{'normal'|static|class}{method|property|non-callable attribute}. concreteness implicit first arg type name comments {unadorned} {unadorned} method def foo(): exists … [View More]now {unadorned} {unadorned} property @property exists now {unadorned} {unadorned} non-callable attribute x = 2 exists now {unadorned} static method @staticmethod exists now {unadorned} static property @staticproperty proposing {unadorned} static non-callable attribute {degenerate case - variables don't have arguments} unnecessary {unadorned} class method @classmethod exists now {unadorned} class property @classproperty or @classmethod;@property proposing {unadorned} class non-callable attribute {degenerate case - variables don't have arguments} unnecessary abc.abstract {unadorned} method @abc.abstractmethod exists now abc.abstract {unadorned} property @abc.abstractproperty exists now abc.abstract {unadorned} non-callable attribute @abc.abstractattribute or @abc.abstract;@attribute proposing abc.abstract static method @abc.abstractstaticmethod exists now abc.abstract static property @abc.staticproperty proposing abc.abstract static non-callable attribute {degenerate case - variables don't have arguments} unnecessary abc.abstract class method @abc.abstractclassmethod exists now abc.abstract class property @abc.abstractclassproperty proposing abc.abstract class non-callable attribute {degenerate case - variables don't have arguments} unnecessary I think the meanings of the new ones are pretty straightforward, but in case they are not... @staticproperty - like @property only without an implicit first argument. Allows the property to be called directly from the class without requiring a throw-away instance. @classproperty - like @property, only the implicit first argument to the method is the class. Allows the property to be called directly from the class without requiring a throw-away instance. @abc.abstractattribute - a simple, non-callable variable that must be overridden in subclasses @abc.abstractstaticproperty - like @abc.abstractproperty only for @staticproperty @abc.abstractclassproperty - like @abc.abstractproperty only for @classproperty --rich [View Less]

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Specify number of items to allocate for array.array() constructor
by Sven Rahmann Feb. 22, 2020

Feb. 22, 2020

At the moment, the array module of the standard library allows to create arrays of different numeric types and to initialize them from an iterable (eg, another array). What's missing is the possiblity to specify the final size of the array (number of items), especially for large arrays. I'm thinking of suffix arrays (a text indexing data structure) for large texts, eg the human genome and its reverse complement (about 6 billion characters from the alphabet ACGT). The suffix array is a long int … [View More]

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Implicit string literal concatenation considered harmful?
by Guido van Rossum March 14, 2018

March 14, 2018

I just spent a few minutes staring at a bug caused by a missing comma -- I got a mysterious argument count error because instead of foo('a', 'b') I had written foo('a' 'b'). This is a fairly common mistake, and IIRC at Google we even had a lint rule against this (there was also a Python dialect used for some specific purpose where this was explicitly forbidden). Now, with modern compiler technology, we can (and in fact do) evaluate compile-time string literal concatenation with the '+' … [View More]

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Re: [Python-ideas] Update the required C compiler for Windows to a supported version.
by Steve Dower March 2, 2014

March 2, 2014

Stephen J. Turnbull wrote: > Vernon D. Cole writes: > >> I cannot compile a Python extension module with any Microsoft compiler >> I can obtain. > > Your pain is understood, but it's not simple to address it. FWIW, I'm working on making the compiler easily obtainable. The VS 2008 link that was posted is unofficial, and could theoretically disappear at any time (I'm not in control of that), but the Windows SDK for Windows 7 and .NET 3.5 SP1 (http://www.microsoft.com/… [View More]en-us/download/details.aspx?id=3138) should be around for as long as Windows 7 is supported. The correct compiler (VC9) is included in this SDK, but unfortunately does not install the vcvarsall.bat file that distutils expects. (Though it's pretty simple to add one that will switch on %1 and call the correct vcvars(86|64|...).bat.) The SDK needed for Python 3.3 and 3.4 (VC10) is even worse - there are many files missing. I'm hoping we'll be able to set up some sort of downloadable package/tool that will fix this. While we'd obviously love to move CPython onto our latest compilers, it's simply not possible (for good reason). Python 3.4 is presumably locked to VC10, but hopefully 3.5 will be able to use whichever version is current when that decision is made. > The basic problem is that the ABI changes. Therefore it's going to require > a complete new set of *all* C extensions for Windows, and the duplication > of download links for all those extensions from quite a few different vendors > is likely to confuse a lot of users. Specifically, the CRT changes. The CRT is an interesting mess of data structures that are exposed in header files, which means while you can have multiple CRTs loaded, they cannot touch each other's data structures at all or things will go bad/crash, and there's no nice way to set it up to avoid this (my colleague who currently owns MSVCRT suggested a not-very-nice way to do it, but I don't think it's going to be reliable enough). Python's stable ABI helps, but does not solve this problem. The file APIs are the worst culprits. The layout of FILE* objects can and do change between CRT versions, and file descriptors are simply indices into an array of these objects that is exposed through macros rather than function calls. As a result, you cannot mix either FILE pointers or file descriptors between CRTs. The only safe option is to build with the matching CRT, and for MSVCRT, this means with the matching compiler. It's unfortunate, and the responsible teams are well aware of the limitation, but it's history at this point, so we have no choice but to work with it. Cheers, Steve [View Less]

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while conditional in list comprehension ??
by Wolfgang Maier Feb. 21, 2014

Feb. 21, 2014

Dear all, I guess this is so obvious that someone must have suggested it before: in list comprehensions you can currently exclude items based on the if conditional, e.g.: [n for n in range(1,1000) if n % 4 == 0] Why not extend this filtering by allowing a while statement in addition to if, as in: [n for n in range(1,1000) while n < 400] Trivial effect, I agree, in this example since you could achieve the same by using range(1,400), but I hope you get the point. This intuitively … [View More]

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Re: [Python-ideas] os.architecture
by Chris Angelico Jan. 2, 2014

Jan. 2, 2014

On Mon, Dec 30, 2013 at 10:39 AM, anatoly techtonik <techtonik(a)gmail.com> wrote: >> download('http://www.libsdl.org/release/SDL2-2.0.1-win32-'+uname()[4])+'.zip') > > Nothing personal, but that code is awful. You're right, it's buggy because I didn't test it. Superfluous close parenthesis there. But my point is that the architecture is right there in the name, so you can save yourself the trouble and just use what comes from uname directly. ChrisA

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"maybe import"?
by Amber Yust Dec. 30, 2013

Dec. 30, 2013

It's a fairly standard pattern to see things like this: try: import foo except ImportError: foo = None (and of course, variants with from...import et cetera). These can potentially add a lot of clutter to the imports section of a file, given that it requires 4 lines to do a conditional import. It seems like it'd be useful and clean to have a syntax that looked like this: maybe import foo from bar maybe import baz from qux maybe import quy as quz Where … [View More]

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Re: [Python-ideas] os.architecture
by Chris Angelico Dec. 30, 2013

Dec. 30, 2013

On Mon, Dec 30, 2013 at 10:57 AM, anatoly techtonik <techtonik(a)gmail.com> wrote: > On Mon, Dec 30, 2013 at 2:42 AM, Chris Angelico <rosuav(a)gmail.com> wrote: >> On Mon, Dec 30, 2013 at 10:39 AM, anatoly techtonik <techtonik(a)gmail.com> wrote: >>>> download('http://www.libsdl.org/release/SDL2-2.0.1-win32-'+uname()[4])+'.zip') >>> >>> Nothing personal, but that code is awful. >> >> You're right, it's buggy because I didn't … [View More]

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os.architecture
by anatoly techtonik Dec. 29, 2013

Dec. 29, 2013

if os.architecture == 32: download('http://www.libsdl.org/release/SDL2-2.0.1-win32-x86.zip') else: download('http://www.libsdl.org/release/SDL2-2.0.1-win32-x64.zip') ?

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Determine Windows version in platform module
by Giampaolo Rodola' Dec. 28, 2013

Dec. 28, 2013

Today I was looking for a way to determine whether I was on Windows >= Vista and couldn't find anything so I came up with this [1]. That led me to think about platform module. Honestly I can't see the usefulness of it as it doesn't give you any usable API to figure out what platform version you're on. As such would something like [1] be acceptable for inclusion? [1] http://stackoverflow.com/questions/12471772/what-is-better-way-of-getting-w… --- Giampaolo https://code.google.com/p/psutil/… [View More]

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PEP draft - Composable futures for reactive programming
by Sergii Mikhtoniuk Dec. 28, 2013

Dec. 28, 2013

Hi all, I would very much appreciate your opinion on my proposal for improvement of *concurrent.futures* package. Comparing to other languages such as Scala and C#, Python’s futures significantly fall behind in functionality especially in ability to chain computations and compose different futures without blocking and waiting for result. New packages continue to emerge (*asyncio*) which provide their own futures implementation, making composition even more difficult. Proposed improvement … [View More]

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Re: [Python-ideas] "maybe import"?
by Amber Yust Dec. 27, 2013

Dec. 27, 2013

On Thu Dec 26 2013 at 8:57:42 PM, Gregory P. Smith <greg(a)krypto.org> wrote: > Such idioms are common. Though I don't think we should encourage their use. Is this a case of "we shouldn't encourage optional dependencies" or "we shouldn't encourage this kind of idiom as a means of implementing optional dependencies" - and if the latter, what alternative would you point people at instead?

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textwrap.TextWrapper width=None (or Inf)
by Matej Cepl Dec. 26, 2013

Dec. 26, 2013

Hi, I wonder why nobody asked on bugs.python.org for rather obvious functionality of being able to reflow a paragraph to one line? Meaning, that any paragraph would be stripped of all whitespace (etc. ... whatever is configured by the additional parameters of the TextWrapper class) and then joined into long line. I know that ''.join(text.splitlines()) does something similar, but a) it doesn't handle all whitespace munging, b) it just seems like an obvious functionality … [View More]

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Reducing language complexity
by anatoly techtonik Dec. 25, 2013

Dec. 25, 2013

One of the tools to reduce language complexity is "explicitness" or the direct link to help/tutorial/documentation from the concept. The problem with most concepts in computer languages that they don't have distinct markers by which you can recognize one feature or another. For example, you can't recognize that code is generator based or uses metaclass magic without searching for yield or some references to metaclass through the source file. One of the ways to reduce language complexity for … [View More]

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thoughts on the new 3.4 statistics module
by Wolfgang Dec. 25, 2013

Dec. 25, 2013

First of all: thank you, Steven and everyone else involved, for taking on the task of starting to implement this long-missed (at least by me) feature ! I really hope the module will be a success and grow over time. I have two thoughts at the moment about the implementation that I think may be worth discussing, if it hasn't happened yet (I have to admit I did not go through all previous posts on this topic, only read the PEP): First: I am not entirely convinced by when the module raises … [View More]Errors. In some places its undoubtedly justified to raise StatisticsError (like when empty sequences are passed to mean()). On the other hand, should there really be an error, when for example no unique value for the mode can be found? Effectively, that would force users to guard every (!) call to the function with try/except. In my opinion, a better choice would be to return float('nan') or even better a module-specific object (call it Undefined or something) that one can check for. This behavior could, in general, be implemented for cases, where input can actually be handled and a result be calculated (like a list of values in the mode example), but this result is considered "undefined" by the algorithm. Second: I am not entirely happy with the three different flavors of the median function. I *do* know that this has been discussed before, but I'm not sure whether *all* alternatives have been considered (the PEP only talks about the median.low, median.high syntax, which, in fact, I wouldn't like that much either. My suggestion would be to have a resolve parameter, by which the behavior of a single median function can be modified. My main argument here is that as the module will grow in the future there will be many more such situations, in which different ways of calculating statistics are all totally acceptable and you would want to leave the choice to the user (the mode function can already be considered as an example: maybe the user would want to have the list of "modes" returned in case that no unambiguous value can be calculated; actually the current code seems to be prepared for later implementation of this feature because it does generate the list, just is not returning it). Now if, in all such situations, the solution is to have extra functions the module will soon end up completely cluttered with them. If, on the other hand, every function that will foreseeably have to handle ambiguous situations had a resolve parameter the module structure would be much clearer. In the median example you would then call median(data) for the default behavior, arguably the interpolation, but median(data, resolve='low') or median(data, resolve='high') for the alternative calculations. Statistically educated users could then guess, relatively easily, which functions have the resolve parameter and a quick look at the function's help could tell them, which arguments are accepted. Finally, let me just point out that these are really just first thoughts and I do understand that these are design decisions about which different people will have different opinions, but I think now is still a good time to discuss them, while with an established and (hopefully :) ) much larger module you will not be able to change things that easily anymore. Hoping for a lively discussion, Wolfgang [View Less]

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Warning on conditionals
by f p Dec. 17, 2013

Dec. 17, 2013

Hi, I'm new here, There are cases of bad use of int or str constants without comparison operators in the if statement as shown in this example: http://stackoverflow.com/questions/20633818/python-if-elif-always-not-worki…. Maybe the case in which the if statement is defeated should rate a warning.

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Pipe indentation
by musicdenotation＠gmail.com Dec. 12, 2013

Dec. 12, 2013

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Slightly changing the signature of the inspect.Parameter constructor
by Antony Lee Dec. 11, 2013

Dec. 11, 2013

It seems to me that POSITIONAL_OR_KEYWORD is the most often used kind of Parameter (after all, this is the "default" kind of Parameter), so perhaps the constructor for Parameter could be changed from def __init__(self, name, kind, *, default=_empty, annotation=_empty, _partial_kwarg=False): to def __init__(self, name, kind=Parameter.POSITIONAL_OR_KEYWORD, *, default=_empty, annotation=_empty, _partial_kwarg=False): Any thoughts on that? Best, Antony

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Automagically set logger name
by Tin Tvrtković Dec. 10, 2013

Dec. 10, 2013

Hello, usually logger instances are retrieved and initialized with the module name, using the well-known pattern: logger = logging.getLogger(__name__) In Java's very popular log4j library (which is cited as an influence by PEP 282), loggers are usually retrieved and initialized in basically an identical way: private final static Logger LOG = Logger.getLogger(<name-of-class>.class); However, in the upcoming log4j 2 library, a new way is available: private final static Logger LOG = … [View More]

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Batching/grouping function for itertools
by Amber Yust Dec. 9, 2013

Dec. 9, 2013

After seeing yet another person asking how to do this on #python (and having needed to do it in the past myself), I'm wondering why itertools doesn't have a function to break an iterator up into N-sized chunks. Existing possible solutions include both the "clever" but somewhat unreadable... batched_iter = zip(*[iter(input_iter)]*n) ...and the long-form... def batch(input_iter, n): input_iter = iter(input_iter) while True: yield [input_iter.next() for _ in … [View More]

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Easily reference a single unittest from cmdline
by Giampaolo Rodola' Dec. 9, 2013

Dec. 9, 2013

During the development process it is very common to implement a new functionality, write a test for it and then run tests. I don't want to run *all* tests though, but only the new one which I just wrote. Currently unittest module lets you do this via cmdline with: python -m unittest test.test_module.TestClass.test_method This is not very practical though as you have to figure out the name of the module (easy) and the name of the test class (something which I *never* remember). Proposal is to … [View More]

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Automatically turning __prepare__ into a classmethod.
by Antony Lee Dec. 9, 2013

Dec. 9, 2013

Just a small idea... __new__ is automagically turned into a staticmethod, because other interpretations don't make sense. Likewise, perhaps __prepare__ could be automagically turned into a classmethod? Antony

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why is not request in httplib pretty printed?
by Matěj Cepl Dec. 7, 2013

Dec. 7, 2013

Hi, looking at http://hg.python.org/cpython/file/543c76769c14/Lib/http/client.py#l847 (but this code has been same since like forever) I see that the HTTP request is NOT pretty printed: if self.debuglevel > 0: print("send:", repr(data)) whereas response in effect (because every header is printed separately) is. Wouldn't it be better to pretty print the request as well? Otherwise I get quite unreadable debugging logs like the following (notice how much response is more … [View More]readable than request). Matěj matej@wycliff: urllib2_kerberos (next *%)$ python test_trac.py send: 'GET /desktopqe-backlog/login HTTP/1.1\r\nAccept-Encoding: identity\r\nHost: someserver.redhat.com\r\nConnection: close\r\nUser-Agent: Python-urllib/2.7\r\n\r\n' reply: 'HTTP/1.1 401 Authorization Required\r\n' header: Date: Fri, 06 Dec 2013 17:11:13 GMT header: Server: Apache header: WWW-Authenticate: Negotiate header: WWW-Authenticate: Basic realm="Kerberos Login" header: Content-Length: 483 header: Connection: close header: Content-Type: text/html; charset=iso-8859-1 2013-12-06 18:11:15,406 DEBUG inside http_error_401 2013-12-06 18:11:15,407 DEBUG retry count: 1 2013-12-06 18:11:15,407 DEBUG req.get_host() returned someserver.redhat.com 2013-12-06 18:11:15,407 DEBUG authGSSClientInit() succeeded 2013-12-06 18:11:15,486 DEBUG authGSSClientStep() succeeded 2013-12-06 18:11:15,486 DEBUG authGSSClientResponse() succeeded send: 'GET /desktopqe-backlog/login HTTP/1.1\r\nAccept-Encoding: identity\r\nHost: someserver.redhat.com\r\nConnection: close\r\nAuthorization: Negotiate YIICdQYJKoZIhvcSA---some-junk--GZDggzt\r\nUser-Agent: Python-urllib/2.7\r\n\r\n' reply: 'HTTP/1.1 302 Found\r\n' header: Date: Fri, 06 Dec 2013 17:11:14 GMT header: Server: Apache header: WWW-Authenticate: Negotiate YIGZBgkqhkiG9xIB--other-junk--NOxMdOR/5 header: Location: https://someserver.redhat.com/desktopqe-backlog header: Content-Length: 0 header: Pragma: no-cache header: Cache-Control: no-cache header: Expires: Fri, 01 Jan 1999 00:00:00 GMT header: Set-Cookie: trac_auth=148d029eb321e9a0782fd30ca3f9d17b; Path=/desktopqe-backlog; secure header: Connection: close header: Content-Type: text/plain; charset=UTF-8 send: 'GET /desktopqe-backlog HTTP/1.1\r\nAccept-Encoding: identity\r\nHost: someserver.redhat.com\r\nConnection: close\r\nUser-Agent: Python-urllib/2.7\r\n\r\n' reply: 'HTTP/1.1 200 OK\r\n' header: Date: Fri, 06 Dec 2013 17:11:15 GMT header: Server: Apache header: Cache-Control: must-revalidate header: Expires: Fri, 01 Jan 1999 00:00:00 GMT header: Content-Length: 9591 header: Set-Cookie: trac_form_token=a6eda80ba3f4ead82093a0af; Path=/desktopqe-backlog; secure header: Set-Cookie: trac_session=213441ab7934999739979a04; expires=Thu, 06-Mar-2014 17:11:15 GMT; Path=/desktopqe-backlog; secure header: Connection: close header: Content-Type: text/html;charset=utf-8 2013-12-06 18:11:17,190 DEBUG www-authenticate header not found 2013-12-06 18:11:17,190 CRITICAL mutual auth failed. No negotiate header matej@wycliff: urllib2_kerberos (next *%)$ [View Less]

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Attribute docstrings [was: One-line abstractmethod function?]
by Stephen J. Turnbull Dec. 7, 2013

Dec. 7, 2013

Reply-To set to python-ideas(a)python.org. Terry Reedy writes: > For data attributes, which are usually mutable, it should be attached to > the attribute *concept*, which is represented by the name, rather than > the current but usually changeable value. Values are usually already > documented either by a value representation or a docstring. This could > be done with a string subclass that is used as needed. > > For methods, the value is nearly always constant.… [View More]

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Replacing the if __name__ == "__main__" idiom (was Re: making a module callable)
by Eric Snow Dec. 6, 2013

Dec. 6, 2013

On Fri, Nov 22, 2013 at 1:44 PM, Gregory P. Smith <greg(a)krypto.org> wrote: > It'd be nice to formalize a way to get rid of the __name__ == '__main__' > idiom as well in the long long run. Sure everyone's editor types that for > them now but it's still a wart. Anyways, digressing... ;) This has come up before and is the subject of several PEPS. [1][2] The current idiom doesn't bother me too much as I try not to have files that are both scripts and modules. However, Python … [View More]

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