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`.

2 files changed, 8 insertions, 0 deletions

diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index 11342a3..181e322 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -1609,6 +1609,8 @@ static PyMethodDef deque_methods[] = {
         METH_FASTCALL,            rotate_doc},
     {"__sizeof__",              (PyCFunction)deque_sizeof,
         METH_NOARGS,             sizeof_doc},
+    {"__class_getitem__",       (PyCFunction)Py_GenericAlias,
+        METH_O|METH_CLASS,       PyDoc_STR("See PEP 585")},
     {NULL,              NULL}   /* sentinel */
 };
 
@@ -2074,6 +2076,8 @@ static PyMethodDef defdict_methods[] = {
      defdict_copy_doc},
     {"__reduce__", (PyCFunction)defdict_reduce, METH_NOARGS,
      reduce_doc},
+    {"__class_getitem__", (PyCFunction)Py_GenericAlias, METH_O|METH_CLASS,
+     PyDoc_STR("See PEP 585")},
     {NULL}
 };
 
diff --git a/Modules/_sre.c b/Modules/_sre.c
index 15950c6..52ed420 100644
--- a/Modules/_sre.c
+++ b/Modules/_sre.c
@@ -2568,6 +2568,8 @@ static PyMethodDef pattern_methods[] = {
     _SRE_SRE_PATTERN_SCANNER_METHODDEF
     _SRE_SRE_PATTERN___COPY___METHODDEF
     _SRE_SRE_PATTERN___DEEPCOPY___METHODDEF
+    {"__class_getitem__", (PyCFunction)Py_GenericAlias, METH_O|METH_CLASS,
+     PyDoc_STR("See PEP 585")},
     {NULL, NULL}
 };
 
@@ -2638,6 +2640,8 @@ static PyMethodDef match_methods[] = {
     _SRE_SRE_MATCH_EXPAND_METHODDEF
     _SRE_SRE_MATCH___COPY___METHODDEF
     _SRE_SRE_MATCH___DEEPCOPY___METHODDEF
+    {"__class_getitem__", (PyCFunction)Py_GenericAlias, METH_O|METH_CLASS,
+     PyDoc_STR("See PEP 585")},
     {NULL, NULL}
 };