Added support for TypedDict inheritance

This is problematic due to CPython bug 42059, but is easily worked around by using class-based declaration instead.
Fixes #101.

docs/userguide.rst

@@ -199,17 +199,22 @@ Type            Notes
 ``Literal``
 ``NamedTuple``  Field values are typechecked
 ``NoReturn``
-``Protocol``    Run-time protocols are checked with :func:`isinstance`, others are
-                ignored
+``Protocol``    Run-time protocols are checked with :func:`isinstance`,
+                others are ignored
 ``Set``         Contents are typechecked
 ``Sequence``    Contents are typechecked
 ``Tuple``       Contents are typechecked
 ``Type``
-``TypedDict``   Contents are typechecked; ``total`` from superclasses is not
-                respected (see `#101`_ for more information)
+``TypedDict``   Contents are typechecked; On Python 3.8 and earlier,
+                ``total`` from superclasses is not respected (see `#101`_ for
+                more information); On Python 3.9.0 or ``typing_extensions``
+                <= 3.7.4.3, false positives can happen when constructing
+                ``TypedDict`` classes using old-style syntax (see
+               `issue 42059`_)
 ``TypeVar``     Constraints, bound types and co/contravariance are supported
                 but custom generic types are not (due to type erasure)
 ``Union``
 =============== =============================================================
 
 .. _#101: https://github.com/agronholm/typeguard/issues/101
+.. _issue 42059: https://bugs.python.org/issue42059

docs/versionhistory.rst

@@ -7,6 +7,8 @@ This library adheres to `Semantic Versioning 2.0 <https://semver.org/#semantic-v
 
 - Added support for Python 3.9 (PR by Csergő Bálint)
 - Added support for nested ``Literal``
+- Added support for ``TypedDict`` inheritance (with some caveats; see the user guide on that for
+  details)
 - An appropriate ``TypeError`` is now raised when encountering an illegal ``Literal`` value
 - Fixed checking ``NoReturn`` on Python < 3.8 when ``typing_extensions`` was not installed
 - Fixed import hook matching unwanted modules (PR by Wouter Bolsterlee)

tests/test_typeguard.py

@@ -27,6 +27,11 @@
 TConstrained = TypeVar('TConstrained', 'Parent', 'Child')
 JSONType = Union[str, int, float, bool, None, List['JSONType'], Dict[str, 'JSONType']]
 
+DummyDict = TypedDict('DummyDict', {'x': int}, total=False)
+issue_42059 = pytest.mark.xfail(bool(DummyDict.__required_keys__),
+                                reason='Fails due to upstream bug BPO-42059')
+del DummyDict
+
 
 class Parent:
     pass
@@ -1242,17 +1247,21 @@ def foo(a: Literal[1, 1.1]):
         pytest.raises(TypeError, foo, 4).match(r"Illegal literal value: 1.1$")
 
     @pytest.mark.parametrize('value, total, error_re', [
-        ({'x': 6, 'y': 'foo'}, True, None),
-        ({'y': 'foo'}, True, r'required key\(s\) \("x"\) missing from argument "arg"'),
-        ({'x': 6, 'y': 3}, True,
-         'type of dict item "y" for argument "arg" must be str; got int instead'),
-        ({'x': 6}, True, r'required key\(s\) \("y"\) missing from argument "arg"'),
-        ({'x': 6}, False, None),
-        ({'x': 'abc'}, False,
-         'type of dict item "x" for argument "arg" must be int; got str instead'),
-        ({'x': 6, 'foo': 'abc'}, False, r'extra key\(s\) \("foo"\) in argument "arg"'),
-    ], ids=['correct', 'missing_x', 'wrong_y', 'missing_y_error', 'missing_y_ok', 'wrong_x',
-            'unknown_key'])
+        pytest.param({'x': 6, 'y': 'foo'}, True, None, id='correct'),
+        pytest.param({'y': 'foo'}, True, r'required key\(s\) \("x"\) missing from argument "arg"',
+                     id='missing_x'),
+        pytest.param({'x': 6, 'y': 3}, True,
+                     'type of dict item "y" for argument "arg" must be str; got int instead',
+                     id='wrong_y'),
+        pytest.param({'x': 6}, True, r'required key\(s\) \("y"\) missing from argument "arg"',
+                     id='missing_y_error'),
+        pytest.param({'x': 6}, False, None, id='missing_y_ok', marks=[issue_42059]),
+        pytest.param({'x': 'abc'}, False,
+                     'type of dict item "x" for argument "arg" must be int; got str instead',
+                     id='wrong_x', marks=[issue_42059]),
+        pytest.param({'x': 6, 'foo': 'abc'}, False, r'extra key\(s\) \("foo"\) in argument "arg"',
+                     id='unknown_key')
+    ])
     def test_typed_dict(self, value, total, error_re):
         DummyDict = TypedDict('DummyDict', {'x': int, 'y': str}, total=total)
 

tests/test_typeguard_py36.py

@@ -6,6 +6,11 @@
 
 from typeguard import TypeChecker, typechecked
 
+try:
+    from typing_extensions import TypedDict
+except ImportError:
+    from typing import TypedDict
+
 
 @runtime_checkable
 class RuntimeProtocol(Protocol):
@@ -87,6 +92,20 @@ def foo() -> AsyncGenerator[int, None]:
 
         foo()
 
+    def test_typeddict_inherited(self):
+        class ParentDict(TypedDict):
+            x: int
+
+        class ChildDict(ParentDict, total=False):
+            y: int
+
+        @typechecked
+        def foo(arg: ChildDict):
+            pass
+
+        foo({'x': 1})
+        pytest.raises(TypeError, foo, {'y': 1})
+
 
 async def asyncgenfunc() -> AsyncGenerator[int, None]:
     yield 1

typeguard/__init__.py

@@ -311,19 +311,22 @@ def check_dict(argname: str, value, expected_type, memo: _TypeCheckMemo) -> None
 
 
 def check_typed_dict(argname: str, value, expected_type, memo: _TypeCheckMemo) -> None:
-    expected_keys = frozenset(expected_type.__annotations__)
-    existing_keys = frozenset(value)
+    declared_keys = frozenset(expected_type.__annotations__)
+    if hasattr(expected_type, '__required_keys__'):
+        required_keys = expected_type.__required_keys__
+    else:  # py3.8 and lower
+        required_keys = declared_keys if expected_type.__total__ else frozenset()
 
-    extra_keys = existing_keys - expected_keys
+    existing_keys = frozenset(value)
+    extra_keys = existing_keys - declared_keys
     if extra_keys:
         keys_formatted = ', '.join('"{}"'.format(key) for key in sorted(extra_keys))
         raise TypeError('extra key(s) ({}) in {}'.format(keys_formatted, argname))
 
-    if expected_type.__total__:
-        missing_keys = expected_keys - existing_keys
-        if missing_keys:
-            keys_formatted = ', '.join('"{}"'.format(key) for key in sorted(missing_keys))
-            raise TypeError('required key(s) ({}) missing from {}'.format(keys_formatted, argname))
+    missing_keys = required_keys - existing_keys
+    if missing_keys:
+        keys_formatted = ', '.join('"{}"'.format(key) for key in sorted(missing_keys))
+        raise TypeError('required key(s) ({}) missing from {}'.format(keys_formatted, argname))
 
     for key, argtype in get_type_hints(expected_type).items():
         argvalue = value.get(key, _missing)