bpo-36921: Deprecate @coroutine for sake of async def (GH-13346)

The second attempt. Now deprecate `@coroutine` only, keep `yield from fut` as is.


https://bugs.python.org/issue36921

Author: asvetlov

Doc/library/asyncio-task.rst

@@ -916,12 +916,13 @@ enforced.
         async def main():
             await old_style_coroutine()
 
-    This decorator is **deprecated** and is scheduled for removal in
-    Python 3.10.
-
     This decorator should not be used for :keyword:`async def`
     coroutines.
 
+    .. deprecated-removed:: 3.8 3.10
+
+       Use :keyword:`async def` instead.
+
 .. function:: iscoroutine(obj)
 
    Return ``True`` if *obj* is a :ref:`coroutine object <coroutine>`.

Lib/asyncio/coroutines.py

@@ -7,6 +7,7 @@
 import sys
 import traceback
 import types
+import warnings
 
 from . import base_futures
 from . import constants
@@ -107,6 +108,9 @@ def coroutine(func):
     If the coroutine is not yielded from before it is destroyed,
     an error message is logged.
     """
+    warnings.warn('"@coroutine" decorator is deprecated since Python 3.8, use "async def" instead',
+                  DeprecationWarning,
+                  stacklevel=2)
     if inspect.iscoroutinefunction(func):
         # In Python 3.5 that's all we need to do for coroutines
         # defined with "async def".

Lib/asyncio/locks.py

@@ -3,12 +3,13 @@
 __all__ = ('Lock', 'Event', 'Condition', 'Semaphore', 'BoundedSemaphore')
 
 import collections
+import types
 import warnings
 
 from . import events
 from . import futures
 from . import exceptions
-from .coroutines import coroutine
+from .import coroutines
 
 
 class _ContextManager:
@@ -55,7 +56,7 @@ def __exit__(self, *args):
         # always raises; that's how the with-statement works.
         pass
 
-    @coroutine
+    @types.coroutine
     def __iter__(self):
         # This is not a coroutine.  It is meant to enable the idiom:
         #
@@ -78,6 +79,9 @@ def __iter__(self):
         yield from self.acquire()
         return _ContextManager(self)
 
+    # The flag is needed for legacy asyncio.iscoroutine()
+    __iter__._is_coroutine = coroutines._is_coroutine
+
     async def __acquire_ctx(self):
         await self.acquire()
         return _ContextManager(self)

Lib/asyncio/tasks.py

@@ -23,7 +23,7 @@
 from . import events
 from . import exceptions
 from . import futures
-from .coroutines import coroutine
+from .coroutines import _is_coroutine
 
 # Helper to generate new task names
 # This uses itertools.count() instead of a "+= 1" operation because the latter
@@ -638,7 +638,7 @@ def ensure_future(coro_or_future, *, loop=None):
                         'required')
 
 
-@coroutine
+@types.coroutine
 def _wrap_awaitable(awaitable):
     """Helper for asyncio.ensure_future().
 
@@ -647,6 +647,8 @@ def _wrap_awaitable(awaitable):
     """
     return (yield from awaitable.__await__())
 
+_wrap_awaitable._is_coroutine = _is_coroutine
+
 
 class _GatheringFuture(futures.Future):
     """Helper for gather().

Lib/test/test_asyncio/test_base_events.py

@@ -575,9 +575,8 @@ def zero_error(fut):
     def test_default_exc_handler_coro(self):
         self.loop._process_events = mock.Mock()
 
-        @asyncio.coroutine
-        def zero_error_coro():
-            yield from asyncio.sleep(0.01)
+        async def zero_error_coro():
+            await asyncio.sleep(0.01)
             1/0
 
         # Test Future.__del__
@@ -723,8 +722,7 @@ def test_set_task_factory(self):
         class MyTask(asyncio.Task):
             pass
 
-        @asyncio.coroutine
-        def coro():
+        async def coro():
             pass
 
         factory = lambda loop, coro: MyTask(coro, loop=loop)
@@ -779,8 +777,7 @@ def test_create_task(self):
         class MyTask(asyncio.Task):
             pass
 
-        @asyncio.coroutine
-        def test():
+        async def test():
             pass
 
         class EventLoop(base_events.BaseEventLoop):
@@ -830,8 +827,7 @@ def test_run_forever_keyboard_interrupt(self):
         # Python issue #22601: ensure that the temporary task created by
         # run_forever() consumes the KeyboardInterrupt and so don't log
         # a warning
-        @asyncio.coroutine
-        def raise_keyboard_interrupt():
+        async def raise_keyboard_interrupt():
             raise KeyboardInterrupt
 
         self.loop._process_events = mock.Mock()
@@ -849,8 +845,7 @@ def raise_keyboard_interrupt():
     def test_run_until_complete_baseexception(self):
         # Python issue #22429: run_until_complete() must not schedule a pending
         # call to stop() if the future raised a BaseException
-        @asyncio.coroutine
-        def raise_keyboard_interrupt():
+        async def raise_keyboard_interrupt():
             raise KeyboardInterrupt
 
         self.loop._process_events = mock.Mock()
@@ -1070,9 +1065,7 @@ def test_create_connection_multiple_errors(self, m_socket):
         class MyProto(asyncio.Protocol):
             pass
 
-        @asyncio.coroutine
-        def getaddrinfo(*args, **kw):
-            yield from []
+        async def getaddrinfo(*args, **kw):
             return [(2, 1, 6, '', ('107.6.106.82', 80)),
                     (2, 1, 6, '', ('107.6.106.82', 80))]
 
@@ -1191,9 +1184,8 @@ def test_create_connection_no_host_port_sock(self):
         self.assertRaises(ValueError, self.loop.run_until_complete, coro)
 
     def test_create_connection_no_getaddrinfo(self):
-        @asyncio.coroutine
-        def getaddrinfo(*args, **kw):
-            yield from []
+        async def getaddrinfo(*args, **kw):
+            return []
 
         def getaddrinfo_task(*args, **kwds):
             return asyncio.Task(getaddrinfo(*args, **kwds), loop=self.loop)
@@ -1219,8 +1211,7 @@ def getaddrinfo_task(*args, **kwds):
             OSError, self.loop.run_until_complete, coro)
 
     def test_create_connection_multiple(self):
-        @asyncio.coroutine
-        def getaddrinfo(*args, **kw):
+        async def getaddrinfo(*args, **kw):
             return [(2, 1, 6, '', ('0.0.0.1', 80)),
                     (2, 1, 6, '', ('0.0.0.2', 80))]
 
@@ -1247,8 +1238,7 @@ def bind(addr):
 
         m_socket.socket.return_value.bind = bind
 
-        @asyncio.coroutine
-        def getaddrinfo(*args, **kw):
+        async def getaddrinfo(*args, **kw):
             return [(2, 1, 6, '', ('0.0.0.1', 80)),
                     (2, 1, 6, '', ('0.0.0.2', 80))]
 
@@ -1349,8 +1339,7 @@ def test_create_connection_service_name(self, m_socket):
                 self.loop.run_until_complete(coro)
 
     def test_create_connection_no_local_addr(self):
-        @asyncio.coroutine
-        def getaddrinfo(host, *args, **kw):
+        async def getaddrinfo(host, *args, **kw):
             if host == 'example.com':
                 return [(2, 1, 6, '', ('107.6.106.82', 80)),
                         (2, 1, 6, '', ('107.6.106.82', 80))]
@@ -1488,11 +1477,10 @@ def test_create_server_empty_host(self):
         # if host is empty string use None instead
         host = object()
 
-        @asyncio.coroutine
-        def getaddrinfo(*args, **kw):
+        async def getaddrinfo(*args, **kw):
             nonlocal host
             host = args[0]
-            yield from []
+            return []
 
         def getaddrinfo_task(*args, **kwds):
             return asyncio.Task(getaddrinfo(*args, **kwds), loop=self.loop)
@@ -1854,9 +1842,10 @@ def test_accept_connection_exception(self, m_log):
             MyProto, sock, None, None, mock.ANY, mock.ANY)
 
     def test_call_coroutine(self):
-        @asyncio.coroutine
-        def simple_coroutine():
-            pass
+        with self.assertWarns(DeprecationWarning):
+            @asyncio.coroutine
+            def simple_coroutine():
+                pass
 
         self.loop.set_debug(True)
         coro_func = simple_coroutine
@@ -1880,9 +1869,7 @@ def test_log_slow_callbacks(self, m_logger):
         def stop_loop_cb(loop):
             loop.stop()
 
-        @asyncio.coroutine
-        def stop_loop_coro(loop):
-            yield from ()
+        async def stop_loop_coro(loop):
             loop.stop()
 
         asyncio.set_event_loop(self.loop)
@@ -1909,8 +1896,7 @@ def stop_loop_coro(loop):
 class RunningLoopTests(unittest.TestCase):
 
     def test_running_loop_within_a_loop(self):
-        @asyncio.coroutine
-        def runner(loop):
+        async def runner(loop):
             loop.run_forever()
 
         loop = asyncio.new_event_loop()

Lib/test/test_asyncio/test_events.py

@@ -253,12 +253,10 @@ def tearDown(self):
         super().tearDown()
 
     def test_run_until_complete_nesting(self):
-        @asyncio.coroutine
-        def coro1():
-            yield
+        async def coro1():
+            await asyncio.sleep(0)
 
-        @asyncio.coroutine
-        def coro2():
+        async def coro2():
             self.assertTrue(self.loop.is_running())
             self.loop.run_until_complete(coro1())
 
@@ -735,8 +733,7 @@ def test_connect_accepted_socket_ssl_timeout_for_plain_socket(self):
 
     @mock.patch('asyncio.base_events.socket')
     def create_server_multiple_hosts(self, family, hosts, mock_sock):
-        @asyncio.coroutine
-        def getaddrinfo(host, port, *args, **kw):
+        async def getaddrinfo(host, port, *args, **kw):
             if family == socket.AF_INET:
                 return [(family, socket.SOCK_STREAM, 6, '', (host, port))]
             else:
@@ -1662,8 +1659,7 @@ def test_add_fds_after_closing(self):
             loop.add_writer(w, callback)
 
     def test_close_running_event_loop(self):
-        @asyncio.coroutine
-        def close_loop(loop):
+        async def close_loop(loop):
             self.loop.close()
 
         coro = close_loop(self.loop)
@@ -1673,8 +1669,7 @@ def close_loop(loop):
     def test_close(self):
         self.loop.close()
 
-        @asyncio.coroutine
-        def test():
+        async def test():
             pass
 
         func = lambda: False
@@ -2142,7 +2137,8 @@ def test_handle_repr(self):
                         '<Handle cancelled>')
 
         # decorated function
-        cb = asyncio.coroutine(noop)
+        with self.assertWarns(DeprecationWarning):
+            cb = asyncio.coroutine(noop)
         h = asyncio.Handle(cb, (), self.loop)
         self.assertEqual(repr(h),
                         '<Handle noop() at %s:%s>'