Question

How would I write a Python program that would always be looking for user input. I think I would want to have a variable equal to the input and then something different would happen based on what that variable equaled. So if the variable were “w” then it would execute a certain command and keep doing that until it received another input like “d” Then something different would happen but it wouldn’t stop until you hit enter.

Answer 1

If you want to constantly look for an user input you’ll need multithreading.

Example:

import threading
import queue

def console(q):
    while 1:
        cmd = input('> ')
        q.put(cmd)
        if cmd == 'quit':
            break

def action_foo():
    print('--> action foo')

def action_bar():
    print('--> action bar')

def invalid_input():
    print('---> Unknown command')

def main():
    cmd_actions = {'foo': action_foo, 'bar': action_bar}
    cmd_queue = queue.Queue()

    dj = threading.Thread(target=console, args=(cmd_queue,))
    dj.start()

    while 1:
        cmd = cmd_queue.get()
        if cmd == 'quit':
            break
        action = cmd_actions.get(cmd, invalid_input)
        action()

main()

As you’ll see this, will get your messages a little mixed up, something like:

> foo
> --> action foo
bar
> --> action bar
cat
> --> Unknown command
quit

That’s beacuse there are two threads writing to stdoutput at the same time. To sync them there’s going to be need of lock:

import threading
import queue

def console(q, lock):
    while 1:
        input()   # Afther pressing Enter you'll be in "input mode"
        with lock:
            cmd = input('> ')

        q.put(cmd)
        if cmd == 'quit':
            break

def action_foo(lock):
    with lock:
        print('--> action foo')
    # other actions

def action_bar(lock):
    with lock:
        print('--> action bar')

def invalid_input(lock):
    with lock:
        print('--> Unknown command')

def main():
    cmd_actions = {'foo': action_foo, 'bar': action_bar}
    cmd_queue = queue.Queue()
    stdout_lock = threading.Lock()

    dj = threading.Thread(target=console, args=(cmd_queue, stdout_lock))
    dj.start()

    while 1:
        cmd = cmd_queue.get()
        if cmd == 'quit':
            break
        action = cmd_actions.get(cmd, invalid_input)
        action(stdout_lock)

main()

Ok, now it’s better:

    # press Enter
> foo
--> action foo
    # press Enter
> bar
--> action bar
    # press Enter
> cat
--> Unknown command
    # press Enter
> quit

Notice that you’ll need to press Enter before typing a command to enter in “input mode”.