Fixed Dict-derived classes being mistaken for TypedDict on Python 3.10+

Fixes #216.

docs/versionhistory.rst

@@ -6,6 +6,8 @@ This library adheres to `Semantic Versioning 2.0 <https://semver.org/#semantic-v
 **UNRELEASED**
 
 - Fixed ``@typechecked`` replacing abstract properties with regular properties
+- Fixed any generic type subclassing ``Dict`` being mistakenly checked as ``TypedDict`` on
+  Python 3.10
 
 **2.13.0** (2021-10-11)
 

src/typeguard/__init__.py

@@ -61,6 +61,19 @@ def isasyncgenfunction(func):
     from typing import _ForwardRef as ForwardRef
     evaluate_forwardref = ForwardRef._eval_type
 
+if sys.version_info >= (3, 10):
+    from typing import is_typeddict
+elif sys.version_info >= (3, 9):
+    def is_typeddict(tp) -> bool:
+        from typing import _TypedDictMeta
+
+        return isinstance(tp, _TypedDictMeta)
+else:
+    def is_typeddict(tp) -> bool:
+        from typing_extensions import _TypedDictMeta
+
+        return isinstance(tp, _TypedDictMeta)
+
 
 if TYPE_CHECKING:
     _F = TypeVar("_F")
@@ -750,7 +763,7 @@ def check_type(argname: str, value, expected_type, memo: Optional[_TypeCheckMemo
             check_typevar(argname, value, expected_type, memo)
         elif issubclass(expected_type, IO):
             check_io(argname, value, expected_type)
-        elif issubclass(expected_type, dict) and hasattr(expected_type, '__annotations__'):
+        elif is_typeddict(expected_type):
             check_typed_dict(argname, value, expected_type, memo)
         elif getattr(expected_type, '_is_protocol', False):
             check_protocol(argname, value, expected_type)

tests/test_typeguard_py36.py

@@ -1,5 +1,5 @@
 import warnings
-from typing import AsyncGenerator, AsyncIterable, AsyncIterator, Callable
+from typing import Any, AsyncGenerator, AsyncIterable, AsyncIterator, Callable, Dict
 
 import pytest
 from typing_extensions import Protocol, runtime_checkable
@@ -112,6 +112,18 @@ def foo(arg: ChildDict):
         foo({'x': 1})
         pytest.raises(TypeError, foo, {'y': 1})
 
+    def test_mapping_is_not_typeddict(self):
+        """Regression test for #216."""
+
+        class Foo(Dict[str, Any]):
+            pass
+
+        @typechecked
+        def foo(arg: Foo):
+            pass
+
+        foo(Foo({'x': 1}))
+
 
 async def asyncgenfunc() -> AsyncGenerator[int, None]:
     yield 1