How to limit the amount of time a function can run for (add a timeout)?

Question

How to set a limit on the maximum amount of time a function can run for? For example, using time.sleep as a placeholder function, how to limit the amount of time time.sleep can run to a maximum of 5 mins (300 seconds)?

import time

try:
    # As noted above `time.sleep` is a placeholder for a function 
    # which takes 10 minutes to complete.
    time.sleep(600)
except:
    print('took too long')

That is, how can time.sleep(600) above be limited and interrupted after 300 seconds?

Answer 1

On POSIX you have a simple and clean solution available in signal module.

import signal
import time

class Timeout(Exception):
    pass

def handler(sig, frame):
    raise Timeout

signal.signal(signal.SIGALRM, handler)  # register interest in SIGALRM events

signal.alarm(2)  # timeout in 2 seconds
try:
    time.sleep(60)
except Timeout:
    print('took too long')

Caveats:

• Does not work on all platforms, e.g. Windows.
• Does not work in threaded applications, only the main thread.

For other readers where the caveats above are a deal breaker, you will need a more heavyweight approach. The best option is usually to run the code in a separate process (or possibly a thread), and terminate that process if it takes too long. See multiprocessing module for example.