bpo-31033: Add a msg argument to Future.cancel() and Task.cancel() (GH-19979)

1 files changed, 8 insertions, 3 deletions

diff --git a/Lib/asyncio/futures.py b/Lib/asyncio/futures.py
index a3cf379..889f3e6 100644
--- a/Lib/asyncio/futures.py
+++ b/Lib/asyncio/futures.py
@@ -51,6 +51,7 @@ class Future:
     _exception = None
     _loop = None
     _source_traceback = None
+    _cancel_message = None
 
     # This field is used for a dual purpose:
     # - Its presence is a marker to declare that a class implements
@@ -123,7 +124,7 @@ class Future:
             raise RuntimeError("Future object is not initialized.")
         return loop
 
-    def cancel(self):
+    def cancel(self, msg=None):
         """Cancel the future and schedule callbacks.
 
         If the future is already done or cancelled, return False.  Otherwise,
@@ -134,6 +135,7 @@ class Future:
         if self._state != _PENDING:
             return False
         self._state = _CANCELLED
+        self._cancel_message = msg
         self.__schedule_callbacks()
         return True
 
@@ -173,7 +175,9 @@ class Future:
         the future is done and has an exception set, this exception is raised.
         """
         if self._state == _CANCELLED:
-            raise exceptions.CancelledError
+            raise exceptions.CancelledError(
+                '' if self._cancel_message is None else self._cancel_message)
+
         if self._state != _FINISHED:
             raise exceptions.InvalidStateError('Result is not ready.')
         self.__log_traceback = False
@@ -190,7 +194,8 @@ class Future:
         InvalidStateError.
         """
         if self._state == _CANCELLED:
-            raise exceptions.CancelledError
+            raise exceptions.CancelledError(
+                '' if self._cancel_message is None else self._cancel_message)
         if self._state != _FINISHED:
             raise exceptions.InvalidStateError('Exception is not set.')
         self.__log_traceback = False