Merge pull request #11977 from jonathanslenders/asyncio-inputhook

Add asyncio input hook for event loop integration.

IPython/terminal/pt_inputhooks/asyncio.py

@@ -0,0 +1,43 b''
+"""
+Inputhook for running the original asyncio event loop while we're waiting for
+input.
+
+By default, in IPython, we run the prompt with a different asyncio event loop,
+because otherwise we risk that people are freezing the prompt by scheduling bad
+coroutines. E.g., a coroutine that does a while/true and never yield back
+control to the loop. We can't cancel that.
+
+However, sometimes we want the asyncio loop to keep running while waiting for
+a prompt.
+
+The following example will print the numbers from 1 to 10 above the prompt,
+while we are waiting for input. (This works also because we use
+prompt_toolkit`s `patch_stdout`)::
+
+    In [1]: import asyncio
+
+    In [2]: %gui asyncio
+
+    In [3]: async def f():
+       ...:     for i in range(10):
+       ...:         await asyncio.sleep(1)
+       ...:         print(i)
+
+
+    In [4]: asyncio.ensure_future(f())
+
+"""
+import asyncio
+
+# Keep reference to the original asyncio loop, because getting the event loop
+# within the input hook would return the other loop.
+loop = asyncio.get_event_loop()
+
+
+def inputhook(context):
+    def stop():
+        loop.stop()
+
+    loop.add_reader(context.fileno(), stop)
+    context.fileno()
+    loop.run_forever()

IPython/terminal/pt_inputhooks/__init__.py

@@ -1,49 +1,50 b''
 import importlib
 import os
 
 aliases = {
     'qt4': 'qt',
     'gtk2': 'gtk',
 }
 
 backends = [
     'qt', 'qt4', 'qt5',
     'gtk', 'gtk2', 'gtk3',
     'tk',
     'wx',
     'pyglet', 'glut',
-    'osx'
+    'osx',
+    'asyncio'
 ]
 
 registered = {}
 
 def register(name, inputhook):
     """Register the function *inputhook* as an event loop integration."""
     registered[name] = inputhook
 
 class UnknownBackend(KeyError):
     def __init__(self, name):
         self.name = name
 
     def __str__(self):
         return ("No event loop integration for {!r}. "
                 "Supported event loops are: {}").format(self.name,
                                     ', '.join(backends + sorted(registered)))
 
 def get_inputhook_name_and_func(gui):
     if gui in registered:
         return gui, registered[gui]
 
     if gui not in backends:
         raise UnknownBackend(gui)
 
     if gui in aliases:
         return get_inputhook_name_and_func(aliases[gui])
 
     gui_mod = gui
     if gui == 'qt5':
         os.environ['QT_API'] = 'pyqt5'
         gui_mod = 'qt'
 
     mod = importlib.import_module('IPython.terminal.pt_inputhooks.'+gui_mod)
     return gui, mod.inputhook