From a327677905956ae0b239ff430a1346dfe265709e Mon Sep 17 00:00:00 2001
From: Carl Friedrich Bolz-Tereick <cfbolz@gmx.de>
Date: Wed, 29 Jan 2020 16:43:37 +0100
Subject: [PATCH] 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.
---
 Lib/unittest/mock.py                                        | 6 +-----
 .../next/Library/2020-01-29-14-58-27.bpo-39485.Zy3ot6.rst   | 3 +++
 2 files changed, 4 insertions(+), 5 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2020-01-29-14-58-27.bpo-39485.Zy3ot6.rst

diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index a3d8b6eab41..37ea5c7e45c 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 @@ FunctionTypes = (
     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 00000000000..f62c31fc686
--- /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.