gh-83076: 3.8x speed improvement in (Async)Mock instantiation (#100252)

Backports: c5726b727e26b81a267933654cf26b760a90d9aa
Signed-off-by: Chris Withers <chris@simplistix.co.uk>

NEWS.d/2022-12-14-17-37-01.gh-issue-83076.NaYzWT.rst

@@ -0,0 +1 @@
+Instantiation of ``Mock()`` and ``AsyncMock()`` is now 3.8x faster.

mock/mock.py

@@ -414,15 +414,18 @@ class NonCallableMock(Base):
     # necessary.
     _lock = RLock()
 
-    def __new__(cls, *args, **kw):
+    def __new__(
+            cls, spec=None, wraps=None, name=None, spec_set=None,
+            parent=None, _spec_state=None, _new_name='', _new_parent=None,
+            _spec_as_instance=False, _eat_self=None, unsafe=False, **kwargs
+        ):
         # every instance has its own class
         # so we can create magic methods on the
         # class without stomping on other mocks
         bases = (cls,)
         if not issubclass(cls, AsyncMockMixin):
             # Check if spec is an async object or function
-            bound_args = _MOCK_SIG.bind_partial(cls, *args, **kw).arguments
-            spec_arg = bound_args.get('spec_set', bound_args.get('spec'))
+            spec_arg = spec_set or spec
             if spec_arg is not None and _is_async_obj(spec_arg):
                 bases = (AsyncMockMixin, cls)
         new = type(cls.__name__, bases, {'__doc__': cls.__doc__})
@@ -508,10 +511,6 @@ def _mock_add_spec(self, spec, spec_set, _spec_as_instance=False,
         _spec_signature = None
         _spec_asyncs = []
 
-        for attr in dir(spec):
-            if iscoroutinefunction(getattr(spec, attr, None)):
-                _spec_asyncs.append(attr)
-
         if spec is not None and not _is_list(spec):
             if isinstance(spec, type):
                 _spec_class = spec
@@ -521,7 +520,13 @@ def _mock_add_spec(self, spec, spec_set, _spec_as_instance=False,
                                         _spec_as_instance, _eat_self)
             _spec_signature = res and res[1]
 
-            spec = dir(spec)
+            spec_list = dir(spec)
+
+            for attr in spec_list:
+                if iscoroutinefunction(getattr(spec, attr, None)):
+                    _spec_asyncs.append(attr)
+
+            spec = spec_list
 
         __dict__ = self.__dict__
         __dict__['_spec_class'] = _spec_class
@@ -1065,9 +1070,6 @@ def _calls_repr(self, prefix="Calls"):
         return f"\n{prefix}: {safe_repr(self.mock_calls)}."
 
 
-_MOCK_SIG = inspect.signature(NonCallableMock.__init__)
-
-
 class _AnyComparer(list):
     """A list which checks if it contains a call which may have an
     argument of ANY, flipping the components of item and self from
@@ -2172,10 +2174,7 @@ def mock_add_spec(self, spec, spec_set=False):
 
 
 class AsyncMagicMixin(MagicMixin):
-    def __init__(self, *args, **kw):
-        self._mock_set_magics()  # make magic work for kwargs in init
-        _safe_super(AsyncMagicMixin, self).__init__(*args, **kw)
-        self._mock_set_magics()  # fix magic broken by upper level init
+    pass
 
 
 class MagicMock(MagicMixin, Mock):
@@ -2218,6 +2217,10 @@ def __get__(self, obj, _type=None):
         return self.create_mock()
 
 
+_CODE_ATTRS = dir(CodeType)
+_CODE_SIG = inspect.signature(partial(CodeType.__init__, None))
+
+
 class AsyncMockMixin(Base):
     await_count = _delegating_property('await_count')
     await_args = _delegating_property('await_args')
@@ -2235,7 +2238,9 @@ def __init__(self, *args, **kwargs):
         self.__dict__['_mock_await_count'] = 0
         self.__dict__['_mock_await_args'] = None
         self.__dict__['_mock_await_args_list'] = _CallList()
-        code_mock = NonCallableMock(spec_set=CodeType)
+        code_mock = NonCallableMock(spec_set=_CODE_ATTRS)
+        code_mock.__dict__["_spec_class"] = CodeType
+        code_mock.__dict__["_spec_signature"] = _CODE_SIG
         code_mock.co_flags = inspect.CO_COROUTINE
         self.__dict__['__code__'] = code_mock
         self.__dict__['__name__'] = 'AsyncMock'

mock/tests/testasync.py

@@ -306,6 +306,19 @@ def test_spec_normal_methods_on_class_with_mock(self):
         self.assertIsInstance(mock.async_method, AsyncMock)
         self.assertIsInstance(mock.normal_method, Mock)
 
+    def test_spec_async_attributes_instance(self):
+        async_instance = AsyncClass()
+        async_instance.async_func_attr = async_func
+        async_instance.later_async_func_attr = normal_func
+
+        mock_async_instance = Mock(spec_set=async_instance)
+
+        async_instance.later_async_func_attr = async_func
+
+        self.assertIsInstance(mock_async_instance.async_func_attr, AsyncMock)
+        # only the shape of the spec at the time of mock construction matters
+        self.assertNotIsInstance(mock_async_instance.later_async_func_attr, AsyncMock)
+
     def test_spec_mock_type_kw(self):
         def inner_test(mock_type):
             async_mock = mock_type(spec=async_func)