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

[Chris Jerdonek]

On Wed, Nov 22, 2017 at 4:32 PM, Victor Stinner <victor.stinner at gmail.com>
wrote:

> Aha, contextlib.nullcontext() was just added, cool!
>

So is this equivalent to--

    @contextmanager
    def yielding(x):
        yield x

I thought we were against adding one-line functions?

--Chris



>
> https://github.com/python/cpython/commit/0784a2e5b174d2dbf7b144d480559e
> 650c5cf64c
> https://bugs.python.org/issue10049
>
> Victor
>
> 2017-09-09 21:54 GMT+02:00 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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> >> Python-Dev at python.org
> >> https://mail.python.org/mailman/listinfo/python-dev
> >> Unsubscribe:
> >> https://mail.python.org/mailman/options/python-dev/
> victor.stinner%40gmail.com
> >>
> >
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