repeat until keypressed

[Terry Reedy]

On 5/29/2017 12:14 PM, Dennis Lee Bieber wrote:
> On Mon, 29 May 2017 06:14:46 -0700 (PDT), Poul Riis <priisdk at gmail.com>
> declaimed the following:
> 
>> In good old pascal there was this one-liner command:
>> repeat until keypressed
>>
>> Apparently there is no built-in analogue for that in python. I have explored several different possibilities (pyglet, keyboard, curses, ginput (from matplotlib) and others) but not managed to find anything that works the way I want.
>>
> 
> 	What OS?
> 
>> In the following example I just want to replace 'waitforbuttonpress' with something like 'continueuntilbuttonpress' if such a command exists. It could be  a mouseclick or a keystroke from the terminal, for instance 'shift', 'space' or some character.
> 
> 	I'm presuming this "waitforbuttonpress" is a feature of pylab -- but I
> can't be sure as you used the polluting "import *" (Google seems to
> indicate it is matplotlib)
> 
> 	Under Windows one has access to the msvcrt module
> 
> 	if msvcrt.kbhit(): break
> 
> ... But I don't know how this will interact with a graphical window (the
> msvcrt module provides functions for /console/ interaction [kbhit, getch,
> putch, ungetch] and for locking regions of files)

If a tk(inter) window has input focus, the msvcrt console key functions 
do not work.  For instance, when one runs code via IDLE, IDLE's Shell 
gets the focus.  I documented this for IDLE under "IDLE-console 
differences" after someone reported a problem with kbhit on 
Stackoverflow.  I presume it is true for other GUIs.

If one has a tkinter GUI, the following might work:

go = True
def key_pressed(event): go = False
<bind key-pressed event to key_pressed>
while go:
     calculate()
     root.update()  # allow events to be processed

The while-loop can be and in some cases will have to be replaced by 
root.after calls.
-- 
Terry Jan Reedy