gh-101688: Implement types.get_original_bases (#101827)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

1 files changed, 40 insertions, 0 deletions

diff --git a/Doc/library/types.rst b/Doc/library/types.rst
index 27b9846..54887f4 100644
--- a/Doc/library/types.rst
+++ b/Doc/library/types.rst
@@ -82,6 +82,46 @@ Dynamic Type Creation
 
    .. versionadded:: 3.7
 
+.. function:: get_original_bases(cls, /)
+
+    Return the tuple of objects originally given as the bases of *cls* before
+    the :meth:`~object.__mro_entries__` method has been called on any bases
+    (following the mechanisms laid out in :pep:`560`). This is useful for
+    introspecting :ref:`Generics <user-defined-generics>`.
+
+    For classes that have an ``__orig_bases__`` attribute, this
+    function returns the value of ``cls.__orig_bases__``.
+    For classes without the ``__orig_bases__`` attribute, ``cls.__bases__`` is
+    returned.
+
+    Examples::
+
+        from typing import TypeVar, Generic, NamedTuple, TypedDict
+
+        T = TypeVar("T")
+        class Foo(Generic[T]): ...
+        class Bar(Foo[int], float): ...
+        class Baz(list[str]): ...
+        Eggs = NamedTuple("Eggs", [("a", int), ("b", str)])
+        Spam = TypedDict("Spam", {"a": int, "b": str})
+
+        assert Bar.__bases__ == (Foo, float)
+        assert get_original_bases(Bar) == (Foo[int], float)
+
+        assert Baz.__bases__ == (list,)
+        assert get_original_bases(Baz) == (list[str],)
+
+        assert Eggs.__bases__ == (tuple,)
+        assert get_original_bases(Eggs) == (NamedTuple,)
+
+        assert Spam.__bases__ == (dict,)
+        assert get_original_bases(Spam) == (TypedDict,)
+
+        assert int.__bases__ == (object,)
+        assert get_original_bases(int) == (object,)
+
+    .. versionadded:: 3.12
+
 .. seealso::
 
    :pep:`560` - Core support for typing module and generic types