From d24c8287e226ac9983caf6bb826a7b53142ee31f Mon Sep 17 00:00:00 2001
From: Yury Selivanov <yury@magic.io>
Date: Sun, 11 Jun 2017 14:11:47 +0000
Subject: [PATCH] bpo-30508: Don't log exceptions if Task/Future "cancel()"
 method was called. (#2110)

---
 Lib/asyncio/futures.py                |  1 +
 Lib/asyncio/tasks.py                  |  1 +
 Lib/test/test_asyncio/test_futures.py |  8 ++++++++
 Lib/test/test_asyncio/test_tasks.py   | 19 +++++++++++++++++++
 Misc/NEWS                             |  3 +++
 5 files changed, 32 insertions(+)

diff --git a/Lib/asyncio/futures.py b/Lib/asyncio/futures.py
index 9ca8d8458b..60b0d31334 100644
--- a/Lib/asyncio/futures.py
+++ b/Lib/asyncio/futures.py
@@ -240,6 +240,7 @@ class Future:
         change the future's state to cancelled, schedule the callbacks and
         return True.
         """
+        self._log_traceback = False
         if self._state != _PENDING:
             return False
         self._state = _CANCELLED
diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index 89d0989c61..6c43e6830a 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -208,6 +208,7 @@ class Task(futures.Future):
         terminates with a CancelledError exception (even if cancel()
         was not called).
         """
+        self._log_traceback = False
         if self.done():
             return False
         if self._fut_waiter is not None:
diff --git a/Lib/test/test_asyncio/test_futures.py b/Lib/test/test_asyncio/test_futures.py
index c306b77e65..195a006fe6 100644
--- a/Lib/test/test_asyncio/test_futures.py
+++ b/Lib/test/test_asyncio/test_futures.py
@@ -314,6 +314,14 @@ class FutureTests(test_utils.TestCase):
         del fut
         self.assertFalse(m_log.error.called)
 
+    @mock.patch('asyncio.base_events.logger')
+    def test_tb_logger_not_called_after_cancel(self, m_log):
+        fut = asyncio.Future(loop=self.loop)
+        fut.set_exception(Exception())
+        fut.cancel()
+        del fut
+        self.assertFalse(m_log.error.called)
+
     @mock.patch('asyncio.base_events.logger')
     def test_tb_logger_result_unretrieved(self, m_log):
         fut = asyncio.Future(loop=self.loop)
diff --git a/Lib/test/test_asyncio/test_tasks.py b/Lib/test/test_asyncio/test_tasks.py
index b3d0653e82..c419015a08 100644
--- a/Lib/test/test_asyncio/test_tasks.py
+++ b/Lib/test/test_asyncio/test_tasks.py
@@ -1828,6 +1828,25 @@ class TaskTests(test_utils.TestCase):
         })
         mock_handler.reset_mock()
 
+    @mock.patch('asyncio.base_events.logger')
+    def test_tb_logger_not_called_after_cancel(self, m_log):
+        loop = asyncio.new_event_loop()
+        self.set_event_loop(loop)
+
+        @asyncio.coroutine
+        def coro():
+            raise TypeError
+
+        @asyncio.coroutine
+        def runner():
+            task = loop.create_task(coro())
+            yield from asyncio.sleep(0.05, loop=loop)
+            task.cancel()
+            task = None
+
+        loop.run_until_complete(runner())
+        self.assertFalse(m_log.error.called)
+
     @mock.patch('asyncio.coroutines.logger')
     def test_coroutine_never_yielded(self, m_log):
         with set_coroutine_debug(True):
diff --git a/Misc/NEWS b/Misc/NEWS
index 33b7b9ae9d..e8f94451f8 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -56,6 +56,9 @@ Extension Modules
 Library
 -------
 
+- bpo-30508: Don't log exceptions if Task/Future "cancel()" method was
+  called.
+
 - bpo-28556: Updates to typing module: Add generic AsyncContextManager, add
   support for ContextManager on all versions. Original PRs by Jelle Zijlstra
   and Ivan Levkivskyi
-- 
2.50.1