pythongh-87390: Add __unpacked__ attribute to types.GenericAlias

Author: JelleZijlstra

Doc/library/types.rst

@@ -311,6 +311,25 @@ Standard names are defined for the following types:
    .. versionchanged:: 3.9.2
       This type can now be subclassed.
 
+   .. attribute:: __origin__
+
+      The non-parameterized generic class.
+
+   .. attribute:: __args__
+
+      The :class:`tuple` of types which parameterize the generic class.
+
+   .. attribute:: __parameters__
+
+      The :data:`~typing.TypeVar`\ s which serve as type parameters for
+      the generic class.
+
+   .. attribute:: __unpacked__
+
+      A boolean that is true if the alias has been unpacked using the
+      ``*`` operator (see :data:`~typing.TypeVarTuple`).
+
+      .. versionadded:: 3.11
 
 .. class:: UnionType
 

Lib/test/test_genericalias.py

@@ -416,6 +416,12 @@ def __deepcopy__(self, memo):
                 self.assertEqual(copied.__args__, alias.__args__)
                 self.assertEqual(copied.__parameters__, alias.__parameters__)
 
+    def test_unpack(self):
+        alias = tuple[str, ...]
+        self.assertIs(alias.__unpacked__, False)
+        unpacked = (*alias,)[0]
+        self.assertIs(unpacked.__unpacked__, True)
+
     def test_union(self):
         a = typing.Union[list[int], list[str]]
         self.assertEqual(a.__args__, (list[int], list[str]))

Misc/NEWS.d/next/Library/2022-04-29-16-41-08.gh-issue-87390.3LNNCv.rst

@@ -0,0 +1,2 @@
+Add an ``__unpacked__`` attribute to :class:`types.GenericAlias`. Patch by
+Jelle Zijlstra.

Objects/genericaliasobject.c

@@ -426,6 +426,7 @@ ga_vectorcall(PyObject *self, PyObject *const *args,
 static const char* const attr_exceptions[] = {
     "__origin__",
     "__args__",
+    "__unpacked__",
     "__parameters__",
     "__mro_entries__",
     "__reduce_ex__",  // needed so we don't look up object.__reduce_ex__
@@ -567,6 +568,7 @@ static PyMethodDef ga_methods[] = {
 static PyMemberDef ga_members[] = {
     {"__origin__", T_OBJECT, offsetof(gaobject, origin), READONLY},
     {"__args__", T_OBJECT, offsetof(gaobject, args), READONLY},
+    {"__unpacked__", T_BOOL, offsetof(gaobject, starred), READONLY},
     {0}
 };