ch21: simplified asyncio examples with modern API

21-asyncio-py3.7/charfinder/tcp_charfinder.py

@@ -38,26 +38,19 @@ async def handle_queries(reader, writer):  # <3>
 # END TCP_CHARFINDER_TOP
 
 # BEGIN TCP_CHARFINDER_MAIN
-def main(address='127.0.0.1', port=2323):  # <1>
+
+async def main(address='127.0.0.1', port=2323):
     port = int(port)
-    loop = asyncio.get_event_loop()
-    server_coro = asyncio.start_server(handle_queries, address, port,
-                                loop=loop) # <2>
-    server = loop.run_until_complete(server_coro) # <3>
+    server = await asyncio.start_server(       
+        handle_queries, address, port)
 
-    host = server.sockets[0].getsockname()  # <4>
-    print('Serving on {}. Hit CTRL-C to stop.'.format(host))  # <5>
-    try:
-        loop.run_forever()  # <6>
-    except KeyboardInterrupt:  # CTRL+C pressed
-        pass
+    addr = server.sockets[0].getsockname()
+    print(f'Serving on {addr}. Hit CTRL-C to stop.')
 
-    print('Server shutting down.')
-    server.close()  # <7>
-    loop.run_until_complete(server.wait_closed())  # <8>
-    loop.close()  # <9>
+    async with server:
+        await server.serve_forever()
 
 
 if __name__ == '__main__':
-    main(*sys.argv[1:])  # <10>
+    asyncio.run(main(*sys.argv[1:]))  # <10>
 # END TCP_CHARFINDER_MAIN

21-asyncio-py3.7/countdown.py

@@ -17,14 +17,12 @@ async def countdown(label, delay):
         print(f'{dt:7.4f}s \t{tabs}{label} = {n}')
         n -= 1
 
-loop = asyncio.get_event_loop()
-tasks = [
-    loop.create_task(countdown('A', .7)),
-    loop.create_task(countdown('B', 2)),
-    loop.create_task(countdown('C', .3)),
-    loop.create_task(countdown('D', 1)),
+coros = [
+    countdown('A', .7),
+    countdown('B', 2),
+    countdown('C', .3),
+    countdown('D', 1),
 ]
 t0 = time.perf_counter()
-loop.run_until_complete(asyncio.wait(tasks))
-loop.close()
+asyncio.run(asyncio.wait(coros))
 print('━' * 50)