bpo-41792: Add is_typeddict function to typing.py (GH-22254)

Closes issue41792.

Also closes https://github.com/python/typing/issues/751.

2 files changed, 22 insertions, 0 deletions

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index 05140fc..42aa430 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -16,6 +16,7 @@ from typing import Generic, ClassVar, Final, final, Protocol
 from typing import cast, runtime_checkable
 from typing import get_type_hints
 from typing import get_origin, get_args
+from typing import is_typeddict
 from typing import no_type_check, no_type_check_decorator
 from typing import Type
 from typing import NewType
@@ -3900,6 +3901,12 @@ class TypedDictTests(BaseTestCase):
             'voice': str,
         }
 
+    def test_is_typeddict(self):
+        assert is_typeddict(Point2D) is True
+        assert is_typeddict(Union[str, int]) is False
+        # classes, not instances
+        assert is_typeddict(Point2D()) is False
+
 
 class IOTests(BaseTestCase):
 
diff --git a/Lib/typing.py b/Lib/typing.py
index 2aedbeb..8c61bd8 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -103,6 +103,7 @@ __all__ = [
     'get_args',
     'get_origin',
     'get_type_hints',
+    'is_typeddict',
     'NewType',
     'no_type_check',
     'no_type_check_decorator',
@@ -1479,6 +1480,20 @@ def get_args(tp):
     return ()
 
 
+def is_typeddict(tp):
+    """Check if an annotation is a TypedDict class
+
+    For example::
+        class Film(TypedDict):
+            title: str
+            year: int
+
+        is_typeddict(Film)  # => True
+        is_typeddict(Union[list, str])  # => False
+    """
+    return isinstance(tp, _TypedDictMeta)
+
+
 def no_type_check(arg):
     """Decorator to indicate that annotations are not type hints.