Make dataclasses.Field, contextvars.Token, ...

... mailbox.MailBox, and mailbox._ProxyFile generic.

Author: emmatyping

Lib/dataclasses.py

@@ -7,6 +7,7 @@
 import builtins
 import functools
 import _thread
+from types import GenericAlias
 
 
 __all__ = ['dataclass',
@@ -284,6 +285,8 @@ def __set_name__(self, owner, name):
             # it.
             func(self.default, owner, name)
 
+    __class_getitem__ = classmethod(GenericAlias)
+
 
 class _DataclassParams:
     __slots__ = ('init',

Lib/mailbox.py

@@ -18,6 +18,7 @@
 import email.generator
 import io
 import contextlib
+from types import GenericAlias
 try:
     import fcntl
 except ImportError:
@@ -260,6 +261,8 @@ def _dump_message(self, message, target, mangle_from_=False):
         else:
             raise TypeError('Invalid message type: %s' % type(message))
 
+    __class_getitem__ = classmethod(GenericAlias)
+
 
 class Maildir(Mailbox):
     """A qmail-style Maildir mailbox."""
@@ -2015,6 +2018,8 @@ def closed(self):
             return False
         return self._file.closed
 
+    __class_getitem__ = classmethod(GenericAlias)
+
 
 class _PartialFile(_ProxyFile):
     """A read-only wrapper of part of a file."""

Lib/test/test_genericalias.py

@@ -7,6 +7,9 @@
 )
 from collections.abc import *
 from contextlib import AbstractContextManager, AbstractAsyncContextManager
+from contextvars import Token
+from dataclasses import Field
+from mailbox import Mailbox, _PartialFile
 from os import DirEntry
 from re import Pattern, Match
 from types import GenericAlias, MappingProxyType
@@ -31,6 +34,9 @@ def test_subscriptable(self):
                   Reversible,
                   Container, Collection,
                   Callable,
+                  Mailbox, _PartialFile,
+                  Token,
+                  Field,
                   Set, MutableSet,
                   Mapping, MutableMapping, MappingView,
                   KeysView, ItemsView, ValuesView,

Python/context.c

@@ -1179,10 +1179,17 @@ static PyGetSetDef PyContextTokenType_getsetlist[] = {
     {NULL}
 };
 
+static PyMethodDef PyContextTokenType_methods[] = {
+    {"__class_getitem__",    (PyCFunction)Py_GenericAlias,
+    METH_O|METH_CLASS,       PyDoc_STR("See PEP 585")},
+    {NULL}
+};
+
 PyTypeObject PyContextToken_Type = {
     PyVarObject_HEAD_INIT(&PyType_Type, 0)
     "Token",
     sizeof(PyContextToken),
+    .tp_methods = PyContextTokenType_methods,
     .tp_getset = PyContextTokenType_getsetlist,
     .tp_dealloc = (destructor)token_tp_dealloc,
     .tp_getattro = PyObject_GenericGetAttr,