[Python-checkins] Fix asyncio.to_thread() documented return type (GH-20547)

[Kyle Stanley]

https://github.com/python/cpython/commit/2b201369b435a4266bda5b895e3b615dbe28ea6e
commit: 2b201369b435a4266bda5b895e3b615dbe28ea6e
branch: master
author: Kyle Stanley <aeros167 at gmail.com>
committer: GitHub <noreply at github.com>
date: 2020-05-31T00:07:04-07:00
summary:

Fix asyncio.to_thread() documented return type (GH-20547)



When I wrote the documentation for `asyncio.to_thread()`, I mistakenly assumed that `return await loop.run_in_executor(...)` within an async def function would return a Future. In reality, it returns a coroutine.

This likely won't affect typical usage of `asyncio.to_thread()`, but it's important for the documentation to be correct here. In general, we also tend to avoid returning futures from high-level APIs in asyncio.

files:
M Doc/library/asyncio-task.rst
M Lib/asyncio/threads.py

diff --git a/Doc/library/asyncio-task.rst b/Doc/library/asyncio-task.rst
index 847363b134a7a..21824ca537f77 100644
--- a/Doc/library/asyncio-task.rst
+++ b/Doc/library/asyncio-task.rst
@@ -614,8 +614,7 @@ Running in Threads
    allowing context variables from the event loop thread to be accessed in the
    separate thread.
 
-   Return an :class:`asyncio.Future` which represents the eventual result of
-   *func*.
+   Return a coroutine that can be awaited to get the eventual result of *func*.
 
    This coroutine function is primarily intended to be used for executing
    IO-bound functions/methods that would otherwise block the event loop if
diff --git a/Lib/asyncio/threads.py b/Lib/asyncio/threads.py
index 51e0ba95d822e..34b7513a42090 100644
--- a/Lib/asyncio/threads.py
+++ b/Lib/asyncio/threads.py
@@ -17,7 +17,7 @@ async def to_thread(func, /, *args, **kwargs):
     allowing context variables from the main thread to be accessed in the
     separate thread.
 
-    Return an asyncio.Future which represents the eventual result of *func*.
+    Return a coroutine that can be awaited to get the eventual result of *func*.
     """
     loop = events.get_running_loop()
     ctx = contextvars.copy_context()