import mock


target = dict(a=1)

@mock.patch.dict('test_patch_dict.target', dict(b=2))
def test_after_patch():
	assert target == dict(a=2, b=2)

target = dict(a=2)

$ rwt mock pytest -- -m pytest test_patch_dict.py
Collecting mock
  Using cached mock-2.0.0-py2.py3-none-any.whl
Collecting pbr>=0.11 (from mock)
  Using cached pbr-3.0.0-py2.py3-none-any.whl
Collecting six>=1.9 (from mock)
  Using cached six-1.10.0-py2.py3-none-any.whl
Installing collected packages: pbr, six, mock
Successfully installed mock-2.0.0 pbr-3.0.0 six-1.10.0
====================================== test session starts =======================================
platform darwin -- Python 3.6.1, pytest-3.0.5, py-1.4.33, pluggy-0.4.0
rootdir: /Users/jaraco, inifile: 
collected 1 items 

test_patch_dict.py F

============================================ FAILURES ============================================
________________________________________ test_after_patch ________________________________________

    @mock.patch.dict('test_patch_dict.target', dict(b=2))
    def test_after_patch():
>   	assert target == dict(a=2, b=2)
E    assert {'a': 2} == {'a': 2, 'b': 2}
E      Omitting 1 identical items, use -v to show
E      Right contains more items:
E      {'b': 2}
E      Use -v to get the full diff

test_patch_dict.py:8: AssertionError
==================================== 1 failed in 0.05 seconds ====================================

______________________________ ERROR collecting test_patch_dict.py _______________________________
ImportError while importing test module '/Users/jaraco/test_patch_dict.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/var/folders/c6/v7hnmq453xb6p2dbz1gqc6rr0000gn/T/rwt-pcm3552g/mock/mock.py:1197: in _dot_lookup
    return getattr(thing, comp)
E   AttributeError: module 'test_patch_dict' has no attribute 'target'

During handling of the above exception, another exception occurred:
<frozen importlib._bootstrap>:942: in _find_and_load_unlocked
    ???
E   AttributeError: module 'test_patch_dict' has no attribute '__path__'

During handling of the above exception, another exception occurred:
test_patch_dict.py:4: in <module>
    @mock.patch.dict('test_patch_dict.target', dict(b=2))
/var/folders/c6/v7hnmq453xb6p2dbz1gqc6rr0000gn/T/rwt-pcm3552g/mock/mock.py:1708: in __init__
    in_dict = _importer(in_dict)
/var/folders/c6/v7hnmq453xb6p2dbz1gqc6rr0000gn/T/rwt-pcm3552g/mock/mock.py:1210: in _importer
    thing = _dot_lookup(thing, comp, import_path)
/var/folders/c6/v7hnmq453xb6p2dbz1gqc6rr0000gn/T/rwt-pcm3552g/mock/mock.py:1199: in _dot_lookup
    __import__(import_path)
E   ModuleNotFoundError: No module named 'test_patch_dict.target'; 'test_patch_dict' is not a package
!!!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!!!!!!!!!!!!!
==================================== 1 error in 0.41 seconds =====================================

diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index 8f46050462..5328fda417 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -1620,9 +1620,7 @@ class _patch_dict(object):
     """

     def __init__(self, in_dict, values=(), clear=False, **kwargs):
-        if isinstance(in_dict, str):
-            in_dict = _importer(in_dict)
-        self.in_dict = in_dict
+        self.in_dict_name = in_dict
         # support any argument supported by dict(...) constructor
         self.values = dict(values)
         self.values.update(kwargs)
@@ -1649,7 +1647,7 @@ class _patch_dict(object):
             attr_value = getattr(klass, attr)
             if (attr.startswith(patch.TEST_PREFIX) and
                  hasattr(attr_value, "__call__")):
-                decorator = _patch_dict(self.in_dict, self.values, self.clear)
+                decorator = _patch_dict(self.in_dict_name, self.values, self.clear)
                 decorated = decorator(attr_value)
                 setattr(klass, attr, decorated)
         return klass
@@ -1662,7 +1660,11 @@ class _patch_dict(object):

     def _patch_dict(self):
         values = self.values
-        in_dict = self.in_dict
+        if isinstance(self.in_dict_name, str):
+            in_dict = _importer(self.in_dict_name)
+        else:
+            in_dict = self.in_dict_name
+        self.in_dict = in_dict

$ cat t.py
from unittest import mock
import c

target = dict(a=1)

@mock.patch("c.A", "target", "updated")
def test_with_decorator():
    print(f"target inside decorator : {A.target}")

def test_with_context_manager():
    with mock.patch("c.A", "target", "updated"):
        print(f"target inside context : {A.target}")

class A:
    target = "changed"

c.A = A
test_with_decorator()
test_with_context_manager()
xarmariocj89 at DESKTOP-9B6VH3A in ~/workspace/cpython on master*
$ cat c.py
class A:
    target = "original"
mariocj89 at DESKTOP-9B6VH3A in ~/workspace/cpython on master*
$ ./python ./t.py
target inside decorator : changed
target inside context : changed