bpo-36373: Deprecate explicit loop in task and subprocess API (GH-16033)

Author: asvetlov

Doc/library/asyncio-subprocess.rst

@@ -71,6 +71,10 @@ Creating Subprocesses
    See the documentation of :meth:`loop.subprocess_exec` for other
    parameters.
 
+   .. deprecated-removed:: 3.8 3.10
+
+      The *loop* parameter.
+
 .. coroutinefunction:: create_subprocess_shell(cmd, stdin=None, \
                           stdout=None, stderr=None, loop=None, \
                           limit=None, \*\*kwds)
@@ -95,6 +99,10 @@ Creating Subprocesses
    escape whitespace and special shell characters in strings that are going
    to be used to construct shell commands.
 
+   .. deprecated-removed:: 3.8 3.10
+
+      The *loop* parameter.
+
 .. note::
 
    The default asyncio event loop implementation on **Windows** does not

Doc/library/asyncio-task.rst

@@ -334,6 +334,9 @@ Running Tasks Concurrently
    cancellation of one submitted Task/Future to cause other
    Tasks/Futures to be cancelled.
 
+   .. deprecated-removed:: 3.8 3.10
+      The *loop* parameter.
+
    .. _asyncio_example_gather:
 
    Example::
@@ -411,6 +414,9 @@ Shielding From Cancellation
        except CancelledError:
            res = None
 
+   .. deprecated-removed:: 3.8 3.10
+      The *loop* parameter.
+
 
 Timeouts
 ========
@@ -478,22 +484,12 @@ Waiting Primitives
    set concurrently and block until the condition specified
    by *return_when*.
 
-   .. deprecated:: 3.8
-
-      If any awaitable in *aws* is a coroutine, it is automatically
-      scheduled as a Task.  Passing coroutines objects to
-      ``wait()`` directly is deprecated as it leads to
-      :ref:`confusing behavior <asyncio_example_wait_coroutine>`.
-
    Returns two sets of Tasks/Futures: ``(done, pending)``.
 
    Usage::
 
         done, pending = await asyncio.wait(aws)
 
-   .. deprecated-removed:: 3.8 3.10
-      The *loop* parameter.
-
    *timeout* (a float or int), if specified, can be used to control
    the maximum number of seconds to wait before returning.
 
@@ -525,6 +521,17 @@ Waiting Primitives
    Unlike :func:`~asyncio.wait_for`, ``wait()`` does not cancel the
    futures when a timeout occurs.
 
+   .. deprecated:: 3.8
+
+      If any awaitable in *aws* is a coroutine, it is automatically
+      scheduled as a Task.  Passing coroutines objects to
+      ``wait()`` directly is deprecated as it leads to
+      :ref:`confusing behavior <asyncio_example_wait_coroutine>`.
+
+   .. deprecated-removed:: 3.8 3.10
+
+      The *loop* parameter.
+
    .. _asyncio_example_wait_coroutine:
    .. note::
 
@@ -568,6 +575,9 @@ Waiting Primitives
    Raises :exc:`asyncio.TimeoutError` if the timeout occurs before
    all Futures are done.
 
+   .. deprecated-removed:: 3.8 3.10
+      The *loop* parameter.
+
    Example::
 
        for f in as_completed(aws):
@@ -694,6 +704,9 @@ Task Object
    .. versionchanged:: 3.8
       Added the ``name`` parameter.
 
+   .. deprecated-removed:: 3.8 3.10
+      The *loop* parameter.
+
    .. method:: cancel()
 
       Request the Task to be cancelled.

Lib/asyncio/subprocess.py

@@ -224,6 +224,13 @@ async def create_subprocess_shell(cmd, stdin=None, stdout=None, stderr=None,
                                   **kwds):
     if loop is None:
         loop = events.get_event_loop()
+    else:
+        warnings.warn("The loop argument is deprecated since Python 3.8 "
+                      "and scheduled for removal in Python 3.10.",
+                      DeprecationWarning,
+                      stacklevel=2
+        )
+
     protocol_factory = lambda: SubprocessStreamProtocol(limit=limit,
                                                         loop=loop,
                                                         _asyncio_internal=True)
@@ -239,6 +246,12 @@ async def create_subprocess_exec(program, *args, stdin=None, stdout=None,
                                  limit=streams._DEFAULT_LIMIT, **kwds):
     if loop is None:
         loop = events.get_event_loop()
+    else:
+        warnings.warn("The loop argument is deprecated since Python 3.8 "
+                      "and scheduled for removal in Python 3.10.",
+                      DeprecationWarning,
+                      stacklevel=2
+        )
     protocol_factory = lambda: SubprocessStreamProtocol(limit=limit,
                                                         loop=loop,
                                                         _asyncio_internal=True)

Lib/asyncio/tasks.py

@@ -573,10 +573,17 @@ def as_completed(fs, *, loop=None, timeout=None):
     """
     if futures.isfuture(fs) or coroutines.iscoroutine(fs):
         raise TypeError(f"expect a list of futures, not {type(fs).__name__}")
-    loop = loop if loop is not None else events.get_event_loop()
-    todo = {ensure_future(f, loop=loop) for f in set(fs)}
+
     from .queues import Queue  # Import here to avoid circular import problem.
     done = Queue(loop=loop)
+
+    if loop is None:
+        loop = events.get_event_loop()
+    else:
+        warnings.warn("The loop argument is deprecated since Python 3.8, "
+                      "and scheduled for removal in Python 3.10.",
+                      DeprecationWarning, stacklevel=2)
+    todo = {ensure_future(f, loop=loop) for f in set(fs)}
     timeout_handle = None
 
     def _on_timeout():
@@ -733,6 +740,10 @@ def gather(*coros_or_futures, loop=None, return_exceptions=False):
     if not coros_or_futures:
         if loop is None:
             loop = events.get_event_loop()
+        else:
+            warnings.warn("The loop argument is deprecated since Python 3.8, "
+                          "and scheduled for removal in Python 3.10.",
+                          DeprecationWarning, stacklevel=2)
         outer = loop.create_future()
         outer.set_result([])
         return outer
@@ -842,6 +853,10 @@ def shield(arg, *, loop=None):
         except CancelledError:
             res = None
     """
+    if loop is not None:
+        warnings.warn("The loop argument is deprecated since Python 3.8, "
+                      "and scheduled for removal in Python 3.10.",
+                      DeprecationWarning, stacklevel=2)
     inner = ensure_future(arg, loop=loop)
     if inner.done():
         # Shortcut.

Lib/test/test_asyncio/test_streams.py

@@ -855,9 +855,10 @@ def test_read_all_from_pipe_reader(self):
         watcher.attach_loop(self.loop)
         try:
             asyncio.set_child_watcher(watcher)
-            create = asyncio.create_subprocess_exec(*args,
-                                                    pass_fds={wfd},
-                                                    loop=self.loop)
+            create = asyncio.create_subprocess_exec(
+                *args,
+                pass_fds={wfd},
+            )
             proc = self.loop.run_until_complete(create)
             self.loop.run_until_complete(proc.wait())
         finally: