bpo-39481: Implementation for PEP 585 (#18239)

This implements things like `list[int]`,
which returns an object of type `types.GenericAlias`.
This object mostly acts as a proxy for `list`,
but has attributes `__origin__` and `__args__`
that allow recovering the parts (with values `list` and `(int,)`.

There is also an approximate notion of type variables;
e.g. `list[T]` has a `__parameters__` attribute equal to `(T,)`.
Type variables are objects of type `typing.TypeVar`.

1 files changed, 2 insertions, 0 deletions

diff --git a/Objects/setobject.c b/Objects/setobject.c
index 41b9ecd..232ba6d 100644
--- a/Objects/setobject.c
+++ b/Objects/setobject.c
@@ -2132,6 +2132,7 @@ static PyMethodDef set_methods[] = {
      union_doc},
     {"update",          (PyCFunction)set_update,        METH_VARARGS,
      update_doc},
+    {"__class_getitem__", (PyCFunction)Py_GenericAlias, METH_O|METH_CLASS, PyDoc_STR("See PEP 585")},
     {NULL,              NULL}   /* sentinel */
 };
 
@@ -2244,6 +2245,7 @@ static PyMethodDef frozenset_methods[] = {
      symmetric_difference_doc},
     {"union",           (PyCFunction)set_union,         METH_VARARGS,
      union_doc},
+    {"__class_getitem__", (PyCFunction)Py_GenericAlias, METH_O|METH_CLASS, PyDoc_STR("See PEP 585")},
     {NULL,              NULL}   /* sentinel */
 };