[Python-Dev] PEP 492: async/await in Python; version 5

Terry Reedy tjreedy at udel.edu
Wed May 6 03:03:52 CEST 2015

On 5/5/2015 6:25 PM, Yury Selivanov wrote:

> Yes, there is no other popular event loop for 3.4 other
> than asyncio,

There is the tk(inter) event loop which also ships with CPython, and 
which is commonly used.

> that uses coroutines based on generators

Oh ;-) Tkinter event loop is callback based.  AFAIK, so is the asyncio 
event loop, but that is somehow masked by tasks that interface to 
coroutines.  Do you think the 'somehow' could be adapted to work with 
the tkinter loop?

What I do not understand is how io events become event loop Event 
instances.  For tk, keyboard and mouse actions seen by the OS become tk 
Events associated with a widget.  Some widgets generate events. User 
code can also generate (pseudo)events.

My specific use case is to be able to run a program in a separate 
process, but display the output in the gui process -- something like 
this (in Idle, for instance).  (Apologies if this misuses the new keywords.)

async def menu_handler()
     ow = OutputWindow(args)  # tk Widget
     proc = subprocess.Popen (or multiprocessing equivalent)
     out = (stdout from process)
     await for line in out:

I want the handler to not block event processing, and disappear after 
finishing.  Might 492 make this possible someday?  Or would having 'line 
in pipe' or just 'data in pipe' translated to a tk event likely require 
a patch to tk?

Terry Jan Reedy

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