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.
diff --git a/Doc/library/asyncio-task.rst b/Doc/library/asyncio-task.rst
index 847363b..21824ca 100644
--- a/Doc/library/asyncio-task.rst
+++ b/Doc/library/asyncio-task.rst
@@ -614,8 +614,7 @@
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