bpo-32193: Convert asyncio to async/await usage (#4753)

* Convert asyncio/tasks.py to async/await

* Convert asyncio/queues.py to async/await

* Convert asyncio/test_utils.py to async/await

* Convert asyncio/base_subprocess.py to async/await

* Convert asyncio/subprocess.py to async/await

* Convert asyncio/streams.py to async/await

* Fix comments

* Convert asyncio/locks.py to async/await

* Convert asyncio.sleep to async def

* Add a comment

* Add missing news

* Convert stubs from AbstrctEventLoop to async functions

* Convert subprocess_shell/subprocess_exec

* Convert connect_read_pipe/connect_write_pip to async/await syntax

* Convert create_datagram_endpoint

* Convert create_unix_server/create_unix_connection

* Get rid of old style coroutines in unix_events.py

* Convert selector_events.py to async/await

* Convert wait_closed and create_connection

* Drop redundant line

* Convert base_events.py

* Code cleanup

* Drop redundant comments

* Fix indentation

* Add explicit tests for compatibility between old and new coroutines

* Convert windows event loop to use async/await

* Fix double awaiting of async function

* Convert asyncio/locks.py

* Improve docstring

* Convert tests to async/await

* Convert more tests

* Convert more tests

* Convert more tests

* Convert tests

* Improve test

Lib/test/test_asyncio/test_streams.py

@@ -571,11 +571,10 @@ def __init__(self, loop):
                 self.server = None
                 self.loop = loop
 
-            @asyncio.coroutine
-            def handle_client(self, client_reader, client_writer):
-                data = yield from client_reader.readline()
+            async def handle_client(self, client_reader, client_writer):
+                data = await client_reader.readline()
                 client_writer.write(data)
-                yield from client_writer.drain()
+                await client_writer.drain()
                 client_writer.close()
 
             def start(self):
@@ -608,14 +607,13 @@ def stop(self):
                     self.loop.run_until_complete(self.server.wait_closed())
                     self.server = None
 
-        @asyncio.coroutine
-        def client(addr):
-            reader, writer = yield from asyncio.open_connection(
+        async def client(addr):
+            reader, writer = await asyncio.open_connection(
                 *addr, loop=self.loop)
             # send a line
             writer.write(b"hello world!\n")
             # read it back
-            msgback = yield from reader.readline()
+            msgback = await reader.readline()
             writer.close()
             return msgback
 
@@ -645,11 +643,10 @@ def __init__(self, loop, path):
                 self.loop = loop
                 self.path = path
 
-            @asyncio.coroutine
-            def handle_client(self, client_reader, client_writer):
-                data = yield from client_reader.readline()
+            async def handle_client(self, client_reader, client_writer):
+                data = await client_reader.readline()
                 client_writer.write(data)
-                yield from client_writer.drain()
+                await client_writer.drain()
                 client_writer.close()
 
             def start(self):
@@ -674,14 +671,13 @@ def stop(self):
                     self.loop.run_until_complete(self.server.wait_closed())
                     self.server = None
 
-        @asyncio.coroutine
-        def client(path):
-            reader, writer = yield from asyncio.open_unix_connection(
+        async def client(path):
+            reader, writer = await asyncio.open_unix_connection(
                 path, loop=self.loop)
             # send a line
             writer.write(b"hello world!\n")
             # read it back
-            msgback = yield from reader.readline()
+            msgback = await reader.readline()
             writer.close()
             return msgback
 
@@ -782,14 +778,13 @@ def server():
                 clt, _ = sock.accept()
                 clt.close()
 
-        @asyncio.coroutine
-        def client(host, port):
-            reader, writer = yield from asyncio.open_connection(
+        async def client(host, port):
+            reader, writer = await asyncio.open_connection(
                 host, port, loop=self.loop)
 
             while True:
                 writer.write(b"foo\n")
-                yield from writer.drain()
+                await writer.drain()
 
         # Start the server thread and wait for it to be listening.
         thread = threading.Thread(target=server)