Non-Blocking raw_input()

Question

After digging around in SO for a while, I still haven't found a good answer to what I would hope is a fairly common need. Basically I need a main thread to do "stuff" until it receives input and then act on that input, then return to the original "stuff". My problem every time seems to be that my program execution seems to halt completely at the raw input, whether I call it in a thread or anywhere else. Forwarning I'm pretty novice to python, but I'd hope this shouldn't be too nasty to implement. Here is what I'm playing with (pulled from my other question where my threading question was answered handily)

So I'm trying to write a program that looks for keyboard presses and then does something in the main program based upon what the user inputs. I'm trying to run the keyboard listening in a thread and then compare whats in the variable in my main loop, but I don't ever seem to be getting the threaded keyboard input. In the below code, the print maybe updating line never happens, just the else block from the main while loop. What do i need to do so that my main loop is aware of the keys pressed by the user?

import threading
import time

kbdInput = ''
playingID = ''

def kbdListener():
    global kbdInput
    kbdInput = rawInput()
    print "maybe updating...the kbdInput variable is: ",kbdInput

listener = threading.Thread(target=kbdListener)

while True:
    print "kbdInput: ",kbdInput
    print "playingID: ",playingID
    if playingID != kbdInput:
        print "Recieved new keyboard Input. Setting playing ID to keyboard input value"
        playingID = kbdInput
    else:
        print "No input from keyboard detected. Sleeping 2 seconds"
    time.sleep(2)

Dirk van Oosterbosch · Accepted Answer · 2016-12-14 22:00:40Z

If you actually want to keep the while loop going on forever, you will need to create a new thread and start it, each time the old one has finished.

I updated the example in the question to make that work:

import threading
import time

kbdInput = ''
playingID = ''
finished = True

def kbdListener():
    global kbdInput, finished
    kbdInput = raw_input("> ")
    print "maybe updating...the kbdInput variable is: {}".format(kbdInput)
    finished = True

while True:
    print "kbdInput: {}".format(kbdInput)
    print "playingID: {}".format(playingID)
    if playingID != kbdInput:
        print "Received new keyboard Input. Setting playing ID to keyboard input value"
        playingID = kbdInput
    else:
        print "No input from keyboard detected. Sleeping 2 seconds"
    if finished:
        finished = False
        listener = threading.Thread(target=kbdListener)
        listener.start()
    time.sleep(2)

Tuan Anh Hoang-Vu · Accepted Answer · 2015-06-19 04:03:58Z

2

You created a thread but forget to start it:

listener = threading.Thread(target=kbdListener)
listener.start()

answered Jun 19, 2015 at 4:03

Tuan Anh Hoang-Vu

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Comments

SiHa · Accepted Answer · 2015-06-19 07:00:43Z

1

In addition to MydKnight's answer (starting the thread), you need to change rawInput to raw_input, and it needs to be in some sort of while loop otherwise you'll only get one raw_input() logged.

answered Jun 19, 2015 at 7:00

SiHa

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Hester · Accepted Answer · 2017-09-06 12:13:52Z

1

I found the accepted answer didn't work for me - it would still block at raw_input even in a separate thread. However, when I switched the threads around it worked right away.

import threading 

def mainWork():
  while 1:
    #whatever you wanted to do until an input is received

myThread = threading.Thread(target=mainWork)
myThread.start()

while 1:
  input = raw_input()
  #do stuff with input when it is received

answered Sep 6, 2017 at 12:13

Hester

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