bpo-38978: Implement __class_getitem__ for asyncio objects (GH-17491)

https://bugs.python.org/issue38978

Author: isidentical

Lib/asyncio/futures.py

@@ -103,6 +103,9 @@ def __del__(self):
             context['source_traceback'] = self._source_traceback
         self._loop.call_exception_handler(context)
 
+    def __class_getitem__(cls, type):
+        return cls
+
     @property
     def _log_traceback(self):
         return self.__log_traceback

Lib/asyncio/queues.py

@@ -76,6 +76,9 @@ def __repr__(self):
     def __str__(self):
         return f'<{type(self).__name__} {self._format()}>'
 
+    def __class_getitem__(cls, type):
+        return cls
+
     def _format(self):
         result = f'maxsize={self._maxsize!r}'
         if getattr(self, '_queue', None):

Lib/asyncio/tasks.py

@@ -175,6 +175,9 @@ def __del__(self):
             self._loop.call_exception_handler(context)
         super().__del__()
 
+    def __class_getitem__(cls, type):
+        return cls
+
     def _repr_info(self):
         return base_tasks._task_repr_info(self)
 

Misc/NEWS.d/next/Library/2019-12-07-13-40-52.bpo-38978.R3gHZI.rst

@@ -0,0 +1,2 @@
+Implement ``__class_getitem__`` on asyncio objects (Future, Task, Queue).
+Patch by Batuhan Taskaya.

Modules/_asynciomodule.c

@@ -1381,6 +1381,12 @@ FutureObj_finalize(FutureObj *fut)
     PyErr_Restore(error_type, error_value, error_traceback);
 }
 
+static PyObject *
+future_cls_getitem(PyObject *cls, PyObject *type)
+{
+    Py_INCREF(cls);
+    return cls;
+}
 
 static PyAsyncMethods FutureType_as_async = {
     (unaryfunc)future_new_iter,         /* am_await */
@@ -1400,6 +1406,7 @@ static PyMethodDef FutureType_methods[] = {
     _ASYNCIO_FUTURE_DONE_METHODDEF
     _ASYNCIO_FUTURE_GET_LOOP_METHODDEF
     _ASYNCIO_FUTURE__REPR_INFO_METHODDEF
+    {"__class_getitem__", future_cls_getitem, METH_O|METH_CLASS, NULL},
     {NULL, NULL}        /* Sentinel */
 };
 
@@ -2429,6 +2436,13 @@ TaskObj_finalize(TaskObj *task)
     FutureObj_finalize((FutureObj*)task);
 }
 
+static PyObject *
+task_cls_getitem(PyObject *cls, PyObject *type)
+{
+    Py_INCREF(cls);
+    return cls;
+}
+
 static void TaskObj_dealloc(PyObject *);  /* Needs Task_CheckExact */
 
 static PyMethodDef TaskType_methods[] = {
@@ -2449,6 +2463,7 @@ static PyMethodDef TaskType_methods[] = {
     _ASYNCIO_TASK_GET_NAME_METHODDEF
     _ASYNCIO_TASK_SET_NAME_METHODDEF
     _ASYNCIO_TASK_GET_CORO_METHODDEF
+    {"__class_getitem__", task_cls_getitem, METH_O|METH_CLASS, NULL},
     {NULL, NULL}        /* Sentinel */
 };