PEP 559 – Built-in noop()

PEP: 559
Title: Built-in noop()
Author: Barry Warsaw <barry at python.org>
Status: Rejected
Type: Standards Track
Created: 08-Sep-2017
Python-Version: 3.7
Post-History: 09-Sep-2017
Resolution: https://mail.python.org/pipermail/python-dev/2017-September/149438.html

Abstract
Rationale
Implementation
Rejected alternatives
- noop() returns something
References
Copyright

Abstract

This PEP proposes adding a new built-in function called noop() which does nothing but return None.

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 1.

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.

Coghlan’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.