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bpo-34149: Behavior of the min/max with key=None#8328

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rhettinger merged 3 commits intopython:masterfrom
Amper:master
Jul 24, 2018
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bpo-34149: Behavior of the min/max with key=None#8328
rhettinger merged 3 commits intopython:masterfrom
Amper:master

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@Amper Amper commented Jul 18, 2018 •
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https://bugs.python.org/issue34149

I was faced with the fact that the behavior of the functions "min"/"max" and "sorted" is a little different.

For example, this code works fine:

>>> sorted([3, 2, 1], key=None)
[1, 2, 3]

But the same example for "min" and "max" doesn't work:

>>> min([3, 2, 1], key=None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'NoneType' object is not callable

That is why the heapq library has this code:

...
def nsmallest(n, iterable, key=None):
    ...
        if key is None:
            result = min(it, default=sentinel)
        else:
            result = min(it, default=sentinel, key=key)
    ...

At the same time, there are many places where such checks are not performed for the "sorted" function. I think the behavior of the "min" / "max" / "sorted" functions should be unified. That is, they should work as if "None" is the default value for "key".

https://bugs.python.org/issue34149

@Amper Amper requested a review from rhettinger as a code owner July 18, 2018 16:09
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rhettinger commented Jul 21, 2018 •
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Amper, please add a NEWS entry using blurb.py (see the devguide for details).

If Serhiy don't feel strongly enough about this to reject this PR, I'll accept and apply it shortly. I'm persuaded by your idea that min(), max(), nsmallest(), nlargest(), sorted(), and itertools.groupby() should ideally have the same API for key functions. Syncing of those APIs would be a minor improvement. As Serhiy pointed out, this does complicate the type signature a bit, but that is of small concern given that the other four functions listed have already gone down this path.

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rhettinger commented Jul 22, 2018

This also needs a documentation update including a versionchanged directive.

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Amper commented Jul 22, 2018

@rhettinger, ok, i have no experience in this, but I'll try to do it tomorrow

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Amper commented Jul 23, 2018

@rhettinger Is everything done right?

@rhettinger rhettinger merged commit e22072f into python:master Jul 24, 2018
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