From: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com>
Date: Mon, 20 Jul 2020 09:00:51 +0000 (-0700)
Subject: bpo-37703: improve asyncio.gather documentation regarding cancellation (GH-15312)
X-Git-Tag: v3.8.5~2
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=58f59a962180123a6d29ece512d198b365726b33;p=thirdparty%2FPython%2Fcpython.git

bpo-37703: improve asyncio.gather documentation regarding cancellation (GH-15312)


These changes updates the doc to comprehensively mention the behaviour of gather.cancel()

Automerge-Triggered-By: @asvetlov
(cherry picked from commit d42528a3a2c7d79fd2e6c9f2a02f3ce12d44c8cc)

Co-authored-by: Vinay Sharma <vinay04sharma@icloud.com>
---

diff --git a/Doc/library/asyncio-task.rst b/Doc/library/asyncio-task.rst
index 00ce5d4b72bd..c96dde2dde92 100644
--- a/Doc/library/asyncio-task.rst
+++ b/Doc/library/asyncio-task.rst
@@ -385,6 +385,14 @@ Running Tasks Concurrently
       #     Task C: Compute factorial(4)...
       #     Task C: factorial(4) = 24
 
+   .. note::
+      If *return_exceptions* is False, cancelling gather() after it
+      has been marked done won't cancel any submitted awaitables.
+      For instance, gather can be marked done after propagating an
+      exception to the caller, therefore, calling ``gather.cancel()``
+      after catching an exception (raised by one of the awaitables) from
+      gather won't cancel any other awaitables.
+
    .. versionchanged:: 3.7
       If the *gather* itself is cancelled, the cancellation is
       propagated regardless of *return_exceptions*.
diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index 38d982716d46..66e81f9200a3 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -736,6 +736,13 @@ def gather(*coros_or_futures, loop=None, return_exceptions=False):
     the outer Future is *not* cancelled in this case.  (This is to
     prevent the cancellation of one child to cause other children to
     be cancelled.)
+
+    If *return_exceptions* is False, cancelling gather() after it
+    has been marked done won't cancel any submitted awaitables.
+    For instance, gather can be marked done after propagating an
+    exception to the caller, therefore, calling ``gather.cancel()``
+    after catching an exception (raised by one of the awaitables) from
+    gather won't cancel any other awaitables.
     """
     if not coros_or_futures:
         if loop is None:
diff --git a/Misc/NEWS.d/next/Documentation/2019-08-16-20-25-42.bpo-37703.Qm_l_H.rst b/Misc/NEWS.d/next/Documentation/2019-08-16-20-25-42.bpo-37703.Qm_l_H.rst
new file mode 100644
index 000000000000..a1a1c354b168
--- /dev/null
+++ b/Misc/NEWS.d/next/Documentation/2019-08-16-20-25-42.bpo-37703.Qm_l_H.rst
@@ -0,0 +1,2 @@
+Updated Documentation to comprehensively elaborate on the behaviour of
+gather.cancel()