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

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Merged
rhettinger merged 3 commits into from
Jul 24, 2018
Merged

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

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f2f071c
bpo-34149: Behavior of the min/max with key=None
Amper Jul 18, 2018
1e5147e
added news entry
Amper Jul 23, 2018
45dc061
bpo-34149: updated documentation for min/max
Amper Jul 23, 2018
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6 changes: 6 additions & 0 deletions Doc/library/functions.rst
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Expand Up @@ -869,6 +869,9 @@ are always available. They are listed here in alphabetical order.
.. versionadded:: 3.4
The *default* keyword-only argument.

.. versionchanged:: 3.8
The *key* can be ``None``.


.. _func-memoryview:
.. function:: memoryview(obj)
Expand Down Expand Up @@ -903,6 +906,9 @@ are always available. They are listed here in alphabetical order.
.. versionadded:: 3.4
The *default* keyword-only argument.

.. versionchanged:: 3.8
The *key* can be ``None``.


.. function:: next(iterator[, default])

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10 changes: 2 additions & 8 deletions Lib/heapq.py
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Expand Up @@ -468,10 +468,7 @@ def nsmallest(n, iterable, key=None):
if n == 1:
it = iter(iterable)
sentinel = object()
if key is None:
result = min(it, default=sentinel)
else:
result = min(it, default=sentinel, key=key)
result = min(it, default=sentinel, key=key)
return [] if result is sentinel else [result]

# When n>=size, it's faster to use sorted()
Expand Down Expand Up @@ -531,10 +528,7 @@ def nlargest(n, iterable, key=None):
if n == 1:
it = iter(iterable)
sentinel = object()
if key is None:
result = max(it, default=sentinel)
else:
result = max(it, default=sentinel, key=key)
result = max(it, default=sentinel, key=key)
return [] if result is sentinel else [result]

# When n>=size, it's faster to use sorted()
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4 changes: 4 additions & 0 deletions Lib/test/test_builtin.py
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Expand Up @@ -905,6 +905,8 @@ def __getitem__(self, index):
self.assertEqual(max((), default=1, key=neg), 1)
self.assertEqual(max((1, 2), default=3, key=neg), 1)

self.assertEqual(max((1, 2), key=None), 2)

data = [random.randrange(200) for i in range(100)]
keys = dict((elem, random.randrange(50)) for elem in data)
f = keys.__getitem__
Expand Down Expand Up @@ -957,6 +959,8 @@ def __getitem__(self, index):
self.assertEqual(min((), default=1, key=neg), 1)
self.assertEqual(min((1, 2), default=1, key=neg), 2)

self.assertEqual(min((1, 2), key=None), 1)

data = [random.randrange(200) for i in range(100)]
keys = dict((elem, random.randrange(50)) for elem in data)
f = keys.__getitem__
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core and Builtins/2018-07-23-21-49-05.bpo-34149.WSV-_g.rst
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@@ -0,0 +1 @@
Fix min and max functions to get default behavior when key is None.
4 changes: 4 additions & 0 deletions Python/bltinmodule.c
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Expand Up @@ -1639,6 +1639,10 @@ min_max(PyObject *args, PyObject *kwds, int op)
return NULL;
}

if (keyfunc == Py_None) {
keyfunc = NULL;
}

maxitem = NULL; /* the result */
maxval = NULL; /* the value associated with the result */
while (( item = PyIter_Next(it) )) {
Expand Down