[Python-checkins] bpo-34149: Behavior of the min/max with key=None (GH-8328)

[Raymond Hettinger]

https://github.com/python/cpython/commit/e22072fb11246f125aa9ff7629c832b9e2407ef0
commit: e22072fb11246f125aa9ff7629c832b9e2407ef0
branch: master
author: Alexander Marshalov <_ at marshalov.org>
committer: Raymond Hettinger <rhettinger at users.noreply.github.com>
date: 2018-07-23T20:58:21-07:00
summary:

bpo-34149: Behavior of the min/max with key=None (GH-8328)

Improve consistency with the signature for sorted(), heapq.nsmallest(), heapq.nlargest(), and itertools.groupby().

files:
A Misc/NEWS.d/next/Core and Builtins/2018-07-23-21-49-05.bpo-34149.WSV-_g.rst
M Doc/library/functions.rst
M Lib/heapq.py
M Lib/test/test_builtin.py
M Python/bltinmodule.c

diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
index 68a5dce5d09b..e52b0900156e 100644
--- a/Doc/library/functions.rst
+++ b/Doc/library/functions.rst
@@ -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)
@@ -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])
 
diff --git a/Lib/heapq.py b/Lib/heapq.py
index b31f4186cf66..0e3555cf9118 100644
--- a/Lib/heapq.py
+++ b/Lib/heapq.py
@@ -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()
@@ -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()
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index 8f91bc9bf919..233c57935653 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -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__
@@ -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__
diff --git a/Misc/NEWS.d/next/Core and Builtins/2018-07-23-21-49-05.bpo-34149.WSV-_g.rst b/Misc/NEWS.d/next/Core and Builtins/2018-07-23-21-49-05.bpo-34149.WSV-_g.rst
new file mode 100644
index 000000000000..9672bcf8eb33
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2018-07-23-21-49-05.bpo-34149.WSV-_g.rst	
@@ -0,0 +1 @@
+Fix min and max functions to get default behavior when key is None.
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 88a4bf991d88..7bb5687d9ae0 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -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) )) {