bpo-39529: Deprecate creating new event loop in asyncio.get_event_loop() (GH-23554)

asyncio.get_event_loop() emits now a deprecation warning when it creates a new event loop.
In future releases it will became an alias of asyncio.get_running_loop().

4 files changed, 47 insertions, 0 deletions

diff --git a/Doc/library/asyncio-eventloop.rst b/Doc/library/asyncio-eventloop.rst
index 7de5a0a..ca91efe 100644
--- a/Doc/library/asyncio-eventloop.rst
+++ b/Doc/library/asyncio-eventloop.rst
@@ -53,6 +53,11 @@ an event loop:
    Consider also using the :func:`asyncio.run` function instead of using
    lower level functions to manually create and close an event loop.
 
+   .. deprecated:: 3.10
+      Deprecation warning is emitted if there is no running event loop.
+      If future Python releases this function will be an alias of
+      :func:`get_running_loop`.
+
 .. function:: set_event_loop(loop)
 
    Set *loop* as a current event loop for the current OS thread.
diff --git a/Doc/library/asyncio-future.rst b/Doc/library/asyncio-future.rst
index 939d4c1..ef496a2 100644
--- a/Doc/library/asyncio-future.rst
+++ b/Doc/library/asyncio-future.rst
@@ -57,12 +57,20 @@ Future Functions
    .. versionchanged:: 3.5.1
       The function accepts any :term:`awaitable` object.
 
+   .. deprecated:: 3.10
+      Deprecation warning is emitted if *obj* is not a Future-like object
+      and *loop* is not specified and there is no running event loop.
+
 
 .. function:: wrap_future(future, *, loop=None)
 
    Wrap a :class:`concurrent.futures.Future` object in a
    :class:`asyncio.Future` object.
 
+   .. deprecated:: 3.10
+      Deprecation warning is emitted if *future* is not a Future-like object
+      and *loop* is not specified and there is no running event loop.
+
 
 Future Object
 =============
@@ -90,6 +98,10 @@ Future Object
    .. versionchanged:: 3.7
       Added support for the :mod:`contextvars` module.
 
+   .. deprecated:: 3.10
+      Deprecation warning is emitted if *loop* is not specified
+      and there is no running event loop.
+
    .. method:: result()
 
       Return the result of the Future.
diff --git a/Doc/library/asyncio-task.rst b/Doc/library/asyncio-task.rst
index 1ca1b4a..3f54ecb 100644
--- a/Doc/library/asyncio-task.rst
+++ b/Doc/library/asyncio-task.rst
@@ -397,6 +397,11 @@ Running Tasks Concurrently
       If the *gather* itself is cancelled, the cancellation is
       propagated regardless of *return_exceptions*.
 
+   .. deprecated:: 3.10
+      Deprecation warning is emitted if no positional arguments are provided
+      or not all positional arguments are Future-like objects
+      and there is no running event loop.
+
 
 Shielding From Cancellation
 ===========================
@@ -434,6 +439,10 @@ Shielding From Cancellation
        except CancelledError:
            res = None
 
+   .. deprecated:: 3.10
+      Deprecation warning is emitted if *aw* is not Future-like object
+      and there is no running event loop.
+
 
 Timeouts
 ========
@@ -593,6 +602,10 @@ Waiting Primitives
            earliest_result = await coro
            # ...
 
+   .. deprecated:: 3.10
+      Deprecation warning is emitted if not all awaitable objects in the *aws*
+      iterable are Future-like objects and there is no running event loop.
+
 
 Running in Threads
 ==================
@@ -775,6 +788,10 @@ Task Object
    .. deprecated-removed:: 3.8 3.10
       The *loop* parameter.
 
+   .. deprecated:: 3.10
+      Deprecation warning is emitted if *loop* is not specified
+      and there is no running event loop.
+
    .. method:: cancel(msg=None)
 
       Request the Task to be cancelled.
diff --git a/Doc/whatsnew/3.10.rst b/Doc/whatsnew/3.10.rst
index dac44cf..ab0b46f 100644
--- a/Doc/whatsnew/3.10.rst
+++ b/Doc/whatsnew/3.10.rst
@@ -1349,6 +1349,19 @@ Deprecated
   scheduled for removal in Python 3.12.
   (Contributed by Erlend E. Aasland in :issue:`42264`.)
 
+* :func:`asyncio.get_event_loop` emits now a deprecation warning if there is
+  no running event loop. In future it will be an alias of
+  :func:`~asyncio.get_running_loop`.
+  :mod:`asyncio` functions which implicitly create a :class:`~asyncio.Future`
+  or :class:`~asyncio.Task` objects emit now
+  a deprecation warning if there is no running event loop and no explicit
+  *loop* argument is passed: :func:`~asyncio.ensure_future`,
+  :func:`~asyncio.wrap_future`, :func:`~asyncio.gather`,
+  :func:`~asyncio.shield`, :func:`~asyncio.as_completed` and constructors of
+  :class:`~asyncio.Future`, :class:`~asyncio.Task`,
+  :class:`~asyncio.StreamReader`, :class:`~asyncio.StreamReaderProtocol`.
+  (Contributed by Serhiy Storchaka in :issue:`39529`.)
+
 * The undocumented built-in function ``sqlite3.enable_shared_cache`` is now
   deprecated, scheduled for removal in Python 3.12.  Its use is strongly
   discouraged by the SQLite3 documentation.  See `the SQLite3 docs