Python script with loop that detects keyboard input

Question

I have a python script that uses a library to talk to GPIO in a constant loop. How can I detect keyboard input inside the loop and choose to exit the loop?

while True:
        for item in pics[1:]:
                matrix.SetImage(item.im.id, 0, 0)
                time.sleep(.1)

matrix.Clear()

Answer 1

I suggest you use the curses module. It will let you check for keyboard input.

Here is an example. It uses my pigpio library to read the gpios but the gpio library you use will be irrelevant to curses.

#!/usr/bin/env python

# gpio_status.py
# 2015-03-04
# Public Domain

import time
import curses
import atexit

import pigpio 

GPIOS=32

MODES=["INPUT", "OUTPUT", "ALT5", "ALT4", "ALT0", "ALT1", "ALT2", "ALT3"]

def cleanup():
   curses.nocbreak()
   curses.echo()
   curses.endwin()
   pi.stop()

pi = pigpio.pi()

stdscr = curses.initscr()
curses.noecho()
curses.cbreak()

atexit.register(cleanup)

cb = []

for g in range(GPIOS):
   cb.append(pi.callback(g, pigpio.EITHER_EDGE))

stdscr.nodelay(1)

stdscr.addstr(0, 23, "Status of gpios 0-31", curses.A_REVERSE)

while True:

   for g in range(GPIOS):
      tally = cb[g].tally()
      mode = pi.get_mode(g)

      col = (g / 11) * 25
      row = (g % 11) + 2

      stdscr.addstr(row, col, "{:2}".format(g), curses.A_BOLD)

      stdscr.addstr(
         "={} {:>6}: {:<10}".format(pi.read(g), MODES[mode], tally))

   stdscr.refresh()

   time.sleep(0.1)

   c = stdscr.getch()

   if c != curses.ERR:
      break

Answer 2

Can be done with ttyas well, like this:

import tty, sys

tty.setraw(sys.stdin.fileno())
while 1:
    ch = sys.stdin.read(1)
    if ch == 'a':
        print "Wohoo"

This will garble your tty, though, so if you need it for anything later, you need to restore it.

Answer 3

everything i try to post here looks so garbled, it's unreadable . i stripped down the code for the pygame lib and made some discoveries about it

import  pygame, sys
from pygame.locals import*
print("esc key to exit the game window must be focused for this to work")
while True:
    DISPLAYSURF = pygame.display.set_mode((50,10)) 
    while True:                          
        for event in pygame.event.get():
            if event.type == QUIT:       
                pygame.quit()            
                sys.exit()               
            elif event.type == KEYDOWN:
                if event.key == K_ESCAPE:
                    pygame.quit()        
                    sys.exit()           
                print(event.key, end=" ")
#               print(event.key)