Mailman 3 March 2017 - Python-ideas

Add socket utilities for IPv4/6 dual-stack servers
by Giampaolo Rodola' March 5, 2017

March 5, 2017

Some years ago I started working on a patch for the socket module which added a couple of utility functions for being able to easily create a server socket, with the addition of being able to accept both IPv4 and IPv6 connections (as a single socket): https://bugs.python.org/issue17561 Given that not all OSes (Windows, many UNIXes) support this natively, I later submitted a recipe adding a "multiple socket listener" class. https://code.activestate.com/recipes/578504-server-supporting-ipv4-and-… [View More]

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Suggestion: Collection type argument for argparse where nargs != None
by David Mayo March 4, 2017

March 4, 2017

A friend of mine (@bcjbcjbcj on twitter) came up with an idea for an argparse improvement that I'd like to propose for inclusion. Currently, argparse with nargs=<anything but None> collects arguments into a list (or a list of lists in the case of action="append"). I would like to propose adding a "collection type" argument to the store and append actions and to add_argument, consisting of a callable that would be applied to the list of type-converted args before adding them to the … [View More]

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add __contains__ into the "type" object
by 语言破碎处 March 4, 2017

March 4, 2017

where we use types? almost: isinstance(obj, T); # issubclass(S, T); Note that TYPE is SET; if we add __contains__ and __le__ into "type", then things become: obj in T; # S <= T; # if only not misleading to a total ordering example: def __getitems__(self, i): if i in Integral: ... elif i in slice: ... # Save "(,)". Really, I prefer to type "lambda:;" than "()". # I fail to modify the "type" object, … [View More]

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Thank's for your confirmation.
by Yander Martinez March 4, 2017

March 4, 2017

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Delayed Execution via Keyword
by Joseph Hackman March 3, 2017

March 3, 2017

Howdy All! This suggestion is inspired by the question on "Efficient debug logging". I propose a keyword to mark an expression for delayed/lazy execution, for the purposes of standardizing such behavior across the language. The proposed format is: delayed: <expr> i.e. log.info("info is %s", delayed: expensiveFunction()) Unlike 'lambda' which returns a function (so the receiver must be lambda-aware), delayed execution blocks are for all purposes values. The first time the value (rather … [View More]

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Re: [Python-ideas] Optional parameters without default value
by Victor Stinner March 3, 2017

March 3, 2017

In my code, I commonly use a NOT_SET singleton used as default value. I like this name for the test: if arg is NOT_SET: ... ;-) I use that when I want to behave differently when None is passed. And yes, I have such code. Victor Le 2 mars 2017 9:36 AM, "M.-A. Lemburg" <mal(a)egenix.com> a écrit : On 02.03.2017 09:03, Serhiy Storchaka wrote: > Function implemented in Python can have optional parameters with default > value. It also can accept arbitrary number of positional and … [View More]keyword > arguments if use var-positional or var-keyword parameters (*args and > **kwargs). But there is no way to declare an optional parameter that > don't have default value. Currently you need to use the sentinel idiom > for implementing this: > > _sentinel = object() > def get(store, key, default=_sentinel): > if store.exists(key): > return store.retrieve(key) > if default is _sentinel: > raise LookupError > else: > return default > > There are drawback of this: > > * Module's namespace is polluted with sentinel's variables. > > * You need to check for the sentinel before passing it to other function > by accident. > > * Possible name conflicts between sentinels for different functions of > the same module. > > * Since the sentinel is accessible outside of the function, it possible > to pass it to the function. > > * help() of the function shows reprs of default values. "foo(bar=<object > object at 0xb713c698>)" looks ugly. > > > I propose to add a new syntax for optional parameters. If the argument > corresponding to the optional parameter without default value is not > specified, the parameter takes no value. As well as the "*" prefix means > "arbitrary number of positional parameters", the prefix "?" can mean > "single optional parameter". > > Example: > > def get(store, key, ?default): > if store.exists(key): > return store.retrieve(key) > try: > return default > except NameError: > raise LookupError Why a new syntax ? Can't we just have a pre-defined sentinel singleton NoDefault and use that throughout the code (and also special case it in argument parsing/handling)? def get(store, key, default=NoDefault): if store.exists(key): return store.retrieve(key) ... I added a special singleton NotGiven to our mxTools long ago for this purpose. -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Experts (#1, Mar 02 2017) >>> Python Projects, Coaching and Consulting ... http://www.egenix.com/ >>> Python Database Interfaces ... http://products.egenix.com/ >>> Plone/Zope Database Interfaces ... http://zope.egenix.com/ ________________________________________________________________________ ::: We implement business ideas - efficiently in both time and costs ::: eGenix.com Software, Skills and Services GmbH Pastor-Loeh-Str.48 D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg Registered at Amtsgericht Duesseldorf: HRB 46611 http://www.egenix.com/company/contact/ http://www.malemburg.com/ _______________________________________________ Python-ideas mailing list Python-ideas(a)python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/ [View Less]

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Re: [Python-ideas] Optional parameters without default value
by Victor Stinner March 3, 2017

March 3, 2017

I dislike the try/except NameError test to chevk if the parameter is set. Catching NameError is slow. What is the root issue? Function signature in help(func)? If yes, the solution can be a special value understood by inspect.signature(). Should it be possible to pass explicitly the special value? func(optional=special_value)? I think it's ok to allow it. The expected behaviour is to behave as func(). Victor Le 2 mars 2017 9:04 AM, "Serhiy Storchaka" <storchaka(a)gmail.com> a écrit : … [View More]Function implemented in Python can have optional parameters with default value. It also can accept arbitrary number of positional and keyword arguments if use var-positional or var-keyword parameters (*args and **kwargs). But there is no way to declare an optional parameter that don't have default value. Currently you need to use the sentinel idiom for implementing this: _sentinel = object() def get(store, key, default=_sentinel): if store.exists(key): return store.retrieve(key) if default is _sentinel: raise LookupError else: return default There are drawback of this: * Module's namespace is polluted with sentinel's variables. * You need to check for the sentinel before passing it to other function by accident. * Possible name conflicts between sentinels for different functions of the same module. * Since the sentinel is accessible outside of the function, it possible to pass it to the function. * help() of the function shows reprs of default values. "foo(bar=<object object at 0xb713c698>)" looks ugly. I propose to add a new syntax for optional parameters. If the argument corresponding to the optional parameter without default value is not specified, the parameter takes no value. As well as the "*" prefix means "arbitrary number of positional parameters", the prefix "?" can mean "single optional parameter". Example: def get(store, key, ?default): if store.exists(key): return store.retrieve(key) try: return default except NameError: raise LookupError Alternative syntaxes: * "=" not followed by an expression: "def get(store, key, default=)". * The "del" keyword: "def get(store, key, del default)". This feature is orthogonal to supporting positional-only parameters. Optional parameters without default value can be positional-or-keyword, keyword-only or positional-only (if the latter is implemented). _______________________________________________ Python-ideas mailing list Python-ideas(a)python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/ [View Less]

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lazy use for optional import
by Nicolas Cellier March 2, 2017

March 2, 2017

I have seen some interest into lazy functionality implementation. I wondered if it can be linked with optional import. PEP 8 <http://www.python.org/dev/peps/pep-0008/> authoritatively states: Imports are always put at the top of the file, just after any module comments and docstrings, and before module globals and constants. So, if we want to stick to PEP8 with non mandatory import, we have to catch the import errors, or jail the class or function using extra functionnality. Why not … [View More]

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suggestion about the sort() function of the list instance
by qhlonline March 2, 2017

March 2, 2017

Hi, all I have a suggestion that, the sort() member method of the list instance, should return the 'self' as the result of list.sort() call. Now list.sort() returns nothing, so that I can NOT write code like this: res = {item: func(item) for item in item_list.sort()} It feels bad. Regards!

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PEP 8 coding style included in grammar ?
by Mathieu BEAL March 2, 2017

March 2, 2017

I was wondering why the PEP coding style ( https://www.python.org/dev/peps/pep-0008/) is not natively included in python grammar ? For instance, both, *function definition* and *class definition*, are using the same “NAME” token. ((see, https://docs.python.org/3/reference/grammar.html). classdef: 'class' NAME ['(' [arglist] ')'] ':' suite funcdef: 'def' NAME parameters ['->' test] ':' suite Then, we are using libraries like pyflake, flake8, pylint, to check the coding style. It seems … [View More]useful to natively make distinction between NAME of classdef and NAME of funcdef, with something like: classdef: 'class' NAME_CLASS ['(' [arglist] ')'] ':' suite funcdef: 'def' NAME_FUNC parameters ['->' test] ':' suite NAME_CLASS: · Class name should normally use the CapWord convention; NAME_FUNC: · Function name should be lowercase, with words separated by underscore as necessary to improve readability, · mixedCase is allowed; STYLE_CAP_WORDS = r’([A-Z]{1}[a-z]+(_[A-Z]{1}[a-z]+)*)’ STYLE_UNDERSCORE_LOW_WORDS = r’([a-z]+(_[a-z]+)*)’ STYLE_MIXED_CASE = r’([a-z]{1,}([A-Z]{1}[a-z]+)*’) NAME_FUNC = STYLE_LOW_WORDS | STYLE_UNDERSCORE_LOW_WORDS | STYLE_MIXED_CASE NAME_CLASS = STYLE_CAP_WORDS | NAME_FUNC # naming convention for functions may be used in cases where the interface is documented and used primarily as a callable (pep8 source). I didn't find any information about this point in a previous post or elsewhere. Is there any reason for such a choice ? or is it a dark old discussion we never talk about ? Mathieu ------------- import re # Testing the first part of the class def, only. style_cap_words = r'^class ([A-Z]{1}[a-z]+(_?[A-Z]{1}[a-z]+)*)$' compiled_style_cap_words = re.compile(style_cap_words) status_samples = {True:['class Hello', 'class Hel_Lo', # ok if Hel and Lo are 2 words 'class HelLo', # same. ], False:['class HellO', 'class _He', 'class HEllo', 'class HE', 'class H', 'class h', 'class Hell_oo', 'class Hell_', 'class _hell', 'class H_E_L_L_O', 'class _H']} def is_matched(sample, pattern=compiled_style_cap_words): matched = pattern.match(sample) return matched is not None for status, samples in status_samples.items(): for sample in samples: is_correct = status == is_matched(sample) assert is_correct, '%s is not correct, required %s' % (sample, status) [View Less]

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