[Python-Dev] PEP 559 - built-in noop()

[Victor Stinner]

Previous discussion: https://bugs.python.org/issue10049

Issue closed as rejected.

Victor

2017-09-09 14:33 GMT-07:00 Victor Stinner <victor.stinner at gmail.com>:
> I was able to find a real keyboard, so here is a more complete code:
> ---
> class Noop:
>     def __call__(self, *args, **kw):
>         return self
>     def __enter__(self, *args, **kw):
>         return self
>     def __exit__(self, *args):
>         return
>     def __repr__(self):
>         return 'nope'
> ---
>
> Example:
> ---
> noop = Noop()
> print(noop)
> print(noop())
> with noop() as nope:
>     print(nope)
> with noop as well:
>     print(well)
> ---
>
> Output:
> ---
> nope
> nope
> nope
> nope
> ---
>
> IHMO the real question is if we need a Noop.nope() method?
>
> Victor
>
> 2017-09-09 12:54 GMT-07:00 Victor Stinner <victor.stinner at gmail.com>:
>> I always wanted this feature (no kidding).
>>
>> Would it be possible to add support for the context manager?
>>
>> with noop(): ...
>>
>> Maybe noop can be an instance of:
>>
>> class Noop:
>>   def __enter__(self, *args, **kw): return self
>>   def __exit__(self, *args): pass
>>   def __call__(self, *args, **kw): return self
>>
>> Victor
>>
>> Le 9 sept. 2017 11:48 AM, "Barry Warsaw" <barry at python.org> a écrit :
>>>
>>> I couldn’t resist one more PEP from the Core sprint.  I won’t reveal where
>>> or how this one came to me.
>>>
>>> -Barry
>>>
>>> PEP: 559
>>> Title: Built-in noop()
>>> Author: Barry Warsaw <barry at python.org>
>>> Status: Draft
>>> Type: Standards Track
>>> Content-Type: text/x-rst
>>> Created: 2017-09-08
>>> Python-Version: 3.7
>>> Post-History: 2017-09-09
>>>
>>>
>>> Abstract
>>> ========
>>>
>>> This PEP proposes adding a new built-in function called ``noop()`` which
>>> does
>>> nothing but return ``None``.
>>>
>>>
>>> Rationale
>>> =========
>>>
>>> It is trivial to implement a no-op function in Python.  It's so easy in
>>> fact
>>> that many people do it many times over and over again.  It would be useful
>>> in
>>> many cases to have a common built-in function that does nothing.
>>>
>>> One use case would be for PEP 553, where you could set the breakpoint
>>> environment variable to the following in order to effectively disable it::
>>>
>>>     $ setenv PYTHONBREAKPOINT=noop
>>>
>>>
>>> Implementation
>>> ==============
>>>
>>> The Python equivalent of the ``noop()`` function is exactly::
>>>
>>>     def noop(*args, **kws):
>>>         return None
>>>
>>> The C built-in implementation is available as a pull request.
>>>
>>>
>>> Rejected alternatives
>>> =====================
>>>
>>> ``noop()`` returns something
>>> ----------------------------
>>>
>>> YAGNI.
>>>
>>> This is rejected because it complicates the semantics.  For example, if
>>> you
>>> always return both ``*args`` and ``**kws``, what do you return when none
>>> of
>>> those are given?  Returning a tuple of ``((), {})`` is kind of ugly, but
>>> provides consistency.  But you might also want to just return ``None``
>>> since
>>> that's also conceptually what the function was passed.
>>>
>>> Or, what if you pass in exactly one positional argument, e.g. ``noop(7)``.
>>> Do
>>> you return ``7`` or ``((7,), {})``?  And so on.
>>>
>>> The author claims that you won't ever need the return value of ``noop()``
>>> so
>>> it will always return ``None``.
>>>
>>> Coghlin's Dialogs (edited for formatting):
>>>
>>>     My counterargument to this would be ``map(noop, iterable)``,
>>>     ``sorted(iterable, key=noop)``, etc. (``filter``, ``max``, and
>>>     ``min`` all accept callables that accept a single argument, as do
>>>     many of the itertools operations).
>>>
>>>     Making ``noop()`` a useful default function in those cases just
>>>     needs the definition to be::
>>>
>>>        def noop(*args, **kwds):
>>>            return args[0] if args else None
>>>
>>>     The counterargument to the counterargument is that using ``None``
>>>     as the default in all these cases is going to be faster, since it
>>>     lets the algorithm skip the callback entirely, rather than calling
>>>     it and having it do nothing useful.
>>>
>>>
>>> Copyright
>>> =========
>>>
>>> This document has been placed in the public domain.
>>>
>>>
>>> ..
>>>    Local Variables:
>>>    mode: indented-text
>>>    indent-tabs-mode: nil
>>>    sentence-end-double-space: t
>>>    fill-column: 70
>>>    coding: utf-8
>>>    End:
>>>
>>>
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>>>
>>