@@ -1310,6 +1310,8 @@ def __call__(self, func):
             return self.decorate_class(func)
         if inspect.iscoroutinefunction(func):
             return self.decorate_async_callable(func)
+        if inspect.isgeneratorfunction(func):
+            return self.decorate_generator_callable(func)
         return self.decorate_callable(func)
 
 
@@ -1342,8 +1344,26 @@ def decoration_helper(self, patched, args, keywargs):
             yield (args, keywargs)
 
 
+    def decorate_generator_callable(self, func):
+        # NB. Keep the method in sync with decorate_async_callable() and decorate_callable()
+        if hasattr(func, 'patchings'):
+            func.patchings.append(self)
+            return func
+
+        @wraps(func)
+        def patched(*args, **keywargs):
+            with self.decoration_helper(patched,
+                                        args,
+                                        keywargs) as (newargs, newkeywargs):
+                out = yield from func(*newargs, **newkeywargs)
+                return out
+
+        patched.patchings = [self]
+        return patched
+
+
     def decorate_callable(self, func):
-        # NB. Keep the method in sync with decorate_async_callable()
+        # NB. Keep the method in sync with decorate_async_callable() and decorate_generator_callable()
         if hasattr(func, 'patchings'):
             func.patchings.append(self)
             return func
@@ -1360,7 +1380,7 @@ def patched(*args, **keywargs):
 
 
     def decorate_async_callable(self, func):
-        # NB. Keep the method in sync with decorate_callable()
+        # NB. Keep the method in sync with decorate_callable() and decorate_generator_callable()
         if hasattr(func, 'patchings'):
             func.patchings.append(self)
             return func

diff --git a/Lib/unittest/test/testmock/testpatch.py b/Lib/unittest/test/testmock/testpatch.py
@@ -1941,6 +1941,38 @@ def test_cant_set_kwargs_when_passing_a_mock(self):
         def test(): pass
         with self.assertRaises(TypeError):
             test()
+
+    def test_patch_generator_function(self):
+        """
+        Previously patching a generator function did
+        not return a generator function, and indeed
+        the desired patch was not even applied.
+
+        This test shows that the behaviour is now
+        fixed.
+        """
+        list_being_tested = [0, 1]
+
+        def alternative_len(l):
+            return 666
+
+        patch_len = patch('%s.len' % builtin_string, alternative_len)
+
+        @patch_len
+        def example_normal_function():
+            """ A normal function using `return` """
+            return len(list_being_tested)
+
+        @patch_len
+        def example_generator_function():
+            """ A generator function """
+            yield len(list_being_tested)
+
+        out_normal = example_normal_function()
+        out_generator = list(example_generator_function())
+
+        self.assertTrue(out_normal == 666)
+        self.assertTrue(out_generator == [666])
 
 
 if __name__ == '__main__':

diff --git a/Misc/NEWS.d/next/Library/2021-10-07-07-47-52.bpo-44730.xYEqXQ.rst b/Misc/NEWS.d/next/Library/2021-10-07-07-47-52.bpo-44730.xYEqXQ.rst
@@ -0,0 +1 @@
+Allow unittest.mock.patch to patch generator functions
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Allow unittest.mock.patch to patch generator functions