[Python-checkins] bpo-39485: fix corner-case in method-detection of mock (GH-18252)

[Carl Friedrich Bolz-Tereick]

https://github.com/python/cpython/commit/a327677905956ae0b239ff430a1346dfe265709e
commit: a327677905956ae0b239ff430a1346dfe265709e
branch: master
author: Carl Friedrich Bolz-Tereick <cfbolz at gmx.de>
committer: GitHub <noreply at github.com>
date: 2020-01-29T15:43:37Z
summary:

bpo-39485: fix corner-case in method-detection of mock (GH-18252)

Replace check for whether something is a method in the mock module. The
previous version fails on PyPy, because there no method wrappers exist
(everything looks like a regular Python-defined function). Thus the
isinstance(getattr(result, '__get__', None), MethodWrapperTypes) check
returns True for any descriptor, not just methods.

This condition could also return erroneously True in CPython for
C-defined descriptors.

Instead to decide whether something is a method, just check directly
whether it's a function defined on the class. This passes all tests on
CPython and fixes the bug on PyPy.

files:
A Misc/NEWS.d/next/Library/2020-01-29-14-58-27.bpo-39485.Zy3ot6.rst
M Lib/unittest/mock.py

diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index a3d8b6eab41a9..37ea5c7e45c8b 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -2748,7 +2748,7 @@ def _must_skip(spec, entry, is_type):
             continue
         if isinstance(result, (staticmethod, classmethod)):
             return False
-        elif isinstance(getattr(result, '__get__', None), MethodWrapperTypes):
+        elif isinstance(result, FunctionTypes):
             # Normal method => skip if looked up on type
             # (if looked up on instance, self is already skipped)
             return is_type
@@ -2778,10 +2778,6 @@ def __init__(self, spec, spec_set=False, parent=None,
     type(ANY.__eq__),
 )
 
-MethodWrapperTypes = (
-    type(ANY.__eq__.__get__),
-)
-
 
 file_spec = None
 
diff --git a/Misc/NEWS.d/next/Library/2020-01-29-14-58-27.bpo-39485.Zy3ot6.rst b/Misc/NEWS.d/next/Library/2020-01-29-14-58-27.bpo-39485.Zy3ot6.rst
new file mode 100644
index 0000000000000..f62c31fc686ad
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-01-29-14-58-27.bpo-39485.Zy3ot6.rst
@@ -0,0 +1,3 @@
+Fix a bug in :func:`unittest.mock.create_autospec` that would complain about
+the wrong number of arguments for custom descriptors defined in an extension
+module returning functions.