Improved the asyncio-prompt example.

Author: jonathanslenders

examples/prompts/asyncio-prompt.py

@@ -1,6 +1,6 @@
 #!/usr/bin/env python
 """
-(Python >= 3.5)
+(Python >= 3.6)
 This is an example of how to prompt inside an application that uses the asyncio
 eventloop. The ``prompt_toolkit`` library will make sure that when other
 coroutines are writing to stdout, they write above the prompt, not destroying
@@ -19,18 +19,20 @@
 from prompt_toolkit.patch_stdout import patch_stdout
 from prompt_toolkit.shortcuts import PromptSession
 
-loop = asyncio.get_event_loop()
 
 
 async def print_counter():
     """
     Coroutine that prints counters.
     """
-    i = 0
-    while True:
-        print('Counter: %i' % i)
-        i += 1
-        await asyncio.sleep(3)
+    try:
+        i = 0
+        while True:
+            print('Counter: %i' % i)
+            i += 1
+            await asyncio.sleep(3)
+    except asyncio.CancelledError:
+        print('Background task cancelled.')
 
 
 async def interactive_shell():
@@ -49,16 +51,20 @@ async def interactive_shell():
             return
 
 
-def main():
+async def main():
     with patch_stdout():
-        shell_task = asyncio.ensure_future(interactive_shell())
-        background_task = asyncio.gather(print_counter(), return_exceptions=True)
-
-        loop.run_until_complete(shell_task)
-        background_task.cancel()
-        loop.run_until_complete(background_task)
+        background_task = asyncio.create_task(print_counter())
+        try:
+            await interactive_shell()
+        finally:
+            background_task.cancel()
         print('Quitting event loop. Bye.')
 
 
 if __name__ == '__main__':
-    main()
+    try:
+        from asyncio import run
+    except ImportError:
+        asyncio.run_until_complete(main())
+    else:
+        asyncio.run(main())