Fix postponed annotations for TypedDict

This fixes TypedDict to work with get_type_hints and postponed evaluation of annotations across modules.

Author: Kronuz

Lib/test/test_typing.py

@@ -34,6 +34,7 @@
 import types
 
 from test import mod_generics_cache
+from test import typed_dict
 
 
 class BaseTestCase(TestCase):
@@ -2804,6 +2805,9 @@ class Point2D(TypedDict):
     x: int
     y: int
 
+class Bar(typed_dict.Foo, total=False):
+    b: int
+
 class LabelPoint2D(Point2D, Label): ...
 
 class Options(TypedDict, total=False):
@@ -3980,6 +3984,12 @@ def test_is_typeddict(self):
         # classes, not instances
         assert is_typeddict(Point2D()) is False
 
+    def test_get_type_hints(self):
+        self.assertEqual(
+            get_type_hints(Bar),
+            {'a': typing.Optional[int], 'b': int}
+        )
+
 
 class IOTests(BaseTestCase):
 

Lib/test/typed_dict.py

@@ -0,0 +1,19 @@
+"""Script used to test `get_type_hints()` on a class formed by inheriting
+a `TypedDict` with postponed annotations, for bpo-41249, pull request #27017.
+
+This script uses future annotations to postpone a type that won't be available
+on the module inheriting from to `Foo`. The subclass in the other module should
+look something like this:
+
+    class Bar(typed_dict.Foo, total=False):
+        b: int
+"""
+
+from __future__ import annotations
+
+from typing import Optional, TypedDict
+
+OptionalIntType = Optional[int]
+
+class Foo(TypedDict):
+    a: OptionalIntType

Lib/typing.py

@@ -135,16 +135,16 @@
 # legitimate imports of those modules.
 
 
-def _type_convert(arg):
+def _type_convert(arg, module=None):
     """For converting None to type(None), and strings to ForwardRef."""
     if arg is None:
         return type(None)
     if isinstance(arg, str):
-        return ForwardRef(arg)
+        return ForwardRef(arg, module=module)
     return arg
 
 
-def _type_check(arg, msg, is_argument=True):
+def _type_check(arg, msg, is_argument=True, module=None):
     """Check that the argument is a type, and return it (internal helper).
 
     As a special case, accept None and return type(None) instead. Also wrap strings
@@ -160,7 +160,7 @@ def _type_check(arg, msg, is_argument=True):
     if is_argument:
         invalid_generic_forms = invalid_generic_forms + (ClassVar, Final)
 
-    arg = _type_convert(arg)
+    arg = _type_convert(arg, module=module)
     if (isinstance(arg, _GenericAlias) and
             arg.__origin__ in invalid_generic_forms):
         raise TypeError(f"{arg} is not valid as type argument")
@@ -631,9 +631,9 @@ class ForwardRef(_Final, _root=True):
 
     __slots__ = ('__forward_arg__', '__forward_code__',
                  '__forward_evaluated__', '__forward_value__',
-                 '__forward_is_argument__')
+                 '__forward_is_argument__', '__forward_module__')
 
-    def __init__(self, arg, is_argument=True):
+    def __init__(self, arg, is_argument=True, module=None):
         if not isinstance(arg, str):
             raise TypeError(f"Forward reference must be a string -- got {arg!r}")
         try:
@@ -645,6 +645,7 @@ def __init__(self, arg, is_argument=True):
         self.__forward_evaluated__ = False
         self.__forward_value__ = None
         self.__forward_is_argument__ = is_argument
+        self.__forward_module__ = module
 
     def _evaluate(self, globalns, localns, recursive_guard):
         if self.__forward_arg__ in recursive_guard:
@@ -656,6 +657,10 @@ def _evaluate(self, globalns, localns, recursive_guard):
                 globalns = localns
             elif localns is None:
                 localns = globalns
+            if self.__forward_module__ is not None:
+                globalns = getattr(
+                    sys.modules.get(self.__forward_module__, None), '__dict__', globalns
+                )
             type_ =_type_check(
                 eval(self.__forward_code__, globalns, localns),
                 "Forward references must evaluate to types.",
@@ -2234,7 +2239,8 @@ def __new__(cls, name, bases, ns, total=True):
         own_annotation_keys = set(own_annotations.keys())
         msg = "TypedDict('Name', {f0: t0, f1: t1, ...}); each t must be a type"
         own_annotations = {
-            n: _type_check(tp, msg) for n, tp in own_annotations.items()
+            n: _type_check(tp, msg, module=tp_dict.__module__)
+            for n, tp in own_annotations.items()
         }
         required_keys = set()
         optional_keys = set()

Misc/NEWS.d/next/Library/2021-07-04-11-33-34.bpo-41249.sHdwBE.rst

@@ -0,0 +1,2 @@
+Fixes TypedDict to work with get_type_hints() and postponed evaluation of
+annotations across modules.