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

(cherry picked from commit a488879cbaf4b8b52699cadccf73bb4c271bcb29)

Co-authored-by: Andrew Svetlov <andrew.svetlov@gmail.com>

2 files changed, 30 insertions, 2 deletions

diff --git a/Lib/asyncio/subprocess.py b/Lib/asyncio/subprocess.py
index e6c1c8b..ce504b8 100644
--- a/Lib/asyncio/subprocess.py
+++ b/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)
diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index cd4832c..a0cb884 100644
--- a/Lib/asyncio/tasks.py
+++ b/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.