Closes issue 17660. You no longer need to explicitly pass create=True when patching builtin names.

3 files changed, 52 insertions, 4 deletions

diff --git a/Doc/library/unittest.mock.rst b/Doc/library/unittest.mock.rst
index cb72a68..6d4b82b 100644
--- a/Doc/library/unittest.mock.rst
+++ b/Doc/library/unittest.mock.rst
@@ -1031,6 +1031,12 @@ patch
     default because it can be dangerous. With it switched on you can write
     passing tests against APIs that don't actually exist!
 
+    .. note::
+
+        .. versionchanged:: 3.5
+           If you are patching builtins in a module then you don't
+           need to pass `create=True`, it will be added by default.
+
     Patch can be used as a `TestCase` class decorator. It works by
     decorating each test method in the class. This reduces the boilerplate
     code when your test methods share a common patchings set. `patch` finds
@@ -1401,6 +1407,21 @@ It is also possible to stop all patches which have been started by using
 
     Stop all active patches. Only stops patches started with `start`.
 
+.. patch-builtins:
+
+patch builtins
+~~~~~~~~~~~~~~~
+You can patch any builtins within a module. The following example patches
+builtin `ord`:
+
+    >>> @patch('__main__.ord')
+    ... def test(mock_ord):
+    ...     mock_ord.return_value = 101
+    ...     print(ord('c'))
+    ...
+    >>> test()
+    101
+
 
 TEST_PREFIX
 ~~~~~~~~~~~
@@ -2011,7 +2032,7 @@ Mocking context managers with a :class:`MagicMock` is common enough and fiddly
 enough that a helper function is useful.
 
     >>> m = mock_open()
-    >>> with patch('__main__.open', m, create=True):
+    >>> with patch('__main__.open', m):
     ...     with open('foo', 'w') as h:
     ...         h.write('some stuff')
     ...
@@ -2026,7 +2047,7 @@ enough that a helper function is useful.
 
 And for reading files:
 
-    >>> with patch('__main__.open', mock_open(read_data='bibble'), create=True) as m:
+    >>> with patch('__main__.open', mock_open(read_data='bibble')) as m:
     ...     with open('foo') as h:
     ...         result = h.read()
     ...
diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index f1f6522..2dd4ca5 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -27,9 +27,13 @@ __version__ = '1.0'
 import inspect
 import pprint
 import sys
+import builtins
+from types import ModuleType
 from functools import wraps, partial
 
 
+_builtins = {name for name in dir(builtins) if not name.startswith('_')}
+
 BaseExceptions = (BaseException,)
 if 'java' in sys.platform:
     # jython
@@ -1166,6 +1170,9 @@ class _patch(object):
         else:
             local = True
 
+        if name in _builtins and isinstance(target, ModuleType):
+            self.create = True
+
         if not self.create and original is DEFAULT:
             raise AttributeError(
                 "%s does not have the attribute %r" % (target, name)
diff --git a/Lib/unittest/test/testmock/testpatch.py b/Lib/unittest/test/testmock/testpatch.py
index c1bc34f..d941d8a 100644
--- a/Lib/unittest/test/testmock/testpatch.py
+++ b/Lib/unittest/test/testmock/testpatch.py
@@ -377,7 +377,7 @@ class PatchTest(unittest.TestCase):
 
     def test_patchobject_wont_create_by_default(self):
         try:
-            @patch.object(SomeClass, 'frooble', sentinel.Frooble)
+            @patch.object(SomeClass, 'ord', sentinel.Frooble)
             def test():
                 self.fail('Patching non existent attributes should fail')
 
@@ -386,7 +386,27 @@ class PatchTest(unittest.TestCase):
             pass
         else:
             self.fail('Patching non existent attributes should fail')
-        self.assertFalse(hasattr(SomeClass, 'frooble'))
+        self.assertFalse(hasattr(SomeClass, 'ord'))
+
+
+    def test_patch_builtins_without_create(self):
+        @patch(__name__+'.ord')
+        def test_ord(mock_ord):
+            mock_ord.return_value = 101
+            return ord('c')
+
+        @patch(__name__+'.open')
+        def test_open(mock_open):
+            m = mock_open.return_value
+            m.read.return_value = 'abcd'
+
+            fobj = open('doesnotexists.txt')
+            data = fobj.read()
+            fobj.close()
+            return data
+
+        self.assertEqual(test_ord(), 101)
+        self.assertEqual(test_open(), 'abcd')
 
 
     def test_patch_with_static_methods(self):