How to use Python keyboard module to persistently detect input?

Question

I'm trying to write a script so that when I press "0" I will get an output, but I want to work without restarting the script, and I haven't been successful using the keyboard module which I've seen as being the most commonly used for detecting key inputs in Python.

What I have so far is

import keyboard

def goto(linenum):
    global line
    line = linenum
line = 1

if line == 1:
    while True:
        if keyboard.is_pressed('0'):
            print('pressed 0')
            break
        goto(1)

What I tried doing was after the loop breaks to refer back to the beginning of the loop and try again from there, however the script ends after I press 0. If I remove the break then it constantly outputs "pressed 0", which is not what I want to happen.

Adrián Fernández · Accepted Answer · 2022-01-09 19:48:17Z

2

You can use pynput to detect key input.

I would do something like this:

from pynput.keyboard import Key, Listener

def on_press(key):
    if str(key).replace("'","") == '0':
        print('pressed 0')

listener = Listener(on_press=on_press)
listener.start()

Once you start the listener, it will be always waiting for the key press and you can still add code after. In fact, with this example I recommend to add something after, maybe an input() so the script won't close immediately.

answered Jan 9, 2022 at 19:48

Adrián Fernández

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1 Comment

sketch54 Over a year ago

Alright so I gave this a go and it just ends the script instantly with no error or feedback of any kind. Then when I added input() like you suggested, I was getting the kind of feedback I was looking for, thank you.

Sevvy325 · Accepted Answer · 2022-01-09 19:38:34Z

I think there are a few problems going on here.

goto is a pretty bad pattern to use and I don't think there's anything here to make your implementation work. It kinda sounds like you're going for some kind of recursion like approach here where when 0 is pressed, then it does some 'reset' and starts looping again. If that is the case you could do something like this:

def wait_for_zero():
    # wait for press here
    # Should add some sort of exit check too
    # 'reset' logic, if any here
    wait_for_zero()

looping with a weak condition is pretty fast cycling and generally a bad idea without some time delay. This is mentioned in the documentation for keybaord. There also is an example in the documentation for keyboard to wait for a keypress: https://github.com/boppreh/keyboard#waiting-for-a-key-press-one-time

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