Timeout function if it takes too long to finish

Question

I have a shell script that loops through a text file containing URL s that I want to visit and take screenshots of   All this is done and simple  The script initializes a class that when run creates a screenshot of each site in the list  Some sites take a very  very long time to load  and some might not be loaded at all  So I want to wrap the screengrabber-function in a timeout script  making the function return False if it couldn t finish within 10 seconds   I m content with the simplest solution possible  maybe setting a asynchronous timer that will return False after 10 seconds no matter what actually happens inside the function

User · Accepted Answer

The process for timing out an operations is described in the documentation for signal.

The basic idea is to use signal handlers to set an alarm for some time interval and raise an exception once that timer expires.

Note that this will only work on UNIX.

Here's an implementation that creates a decorator (save the following code as timeout.py).

from functools import wraps
import errno
import os
import signal

class TimeoutError(Exception):
    pass

def timeout(seconds=10, error_message=os.strerror(errno.ETIME)):
    def decorator(func):
        def _handle_timeout(signum, frame):
            raise TimeoutError(error_message)

        def wrapper(*args, **kwargs):
            signal.signal(signal.SIGALRM, _handle_timeout)
            signal.alarm(seconds)
            try:
                result = func(*args, **kwargs)
            finally:
                signal.alarm(0)
            return result

        return wraps(func)(wrapper)

    return decorator

This creates a decorator called @timeout that can be applied to any long running functions.

So, in your application code, you can use the decorator like so:

from timeout import timeout

# Timeout a long running function with the default expiry of 10 seconds.
@timeout
def long_running_function1():
    ...

# Timeout after 5 seconds
@timeout(5)
def long_running_function2():
    ...

# Timeout after 30 seconds, with the error "Connection timed out"
@timeout(30, os.strerror(errno.ETIMEDOUT))
def long_running_function3():
    ...

User · Answer

I rewrote David s answer using the with statement  it allows you do do this   with timeout seconds 3       time sleep 4    Which will raise a TimeoutError   The code is still using signal and thus UNIX only   import signal  class timeout      def   init   self  seconds 1  error message  Timeout            self seconds   seconds         self error message   error message     def handle timeout self  signum  frame           raise TimeoutError self error message      def   enter   self           signal signal signal SIGALRM  self handle timeout          signal alarm self seconds      def   exit   self  type  value  traceback           signal alarm 0

[python] Timeout function if it takes too long to finish

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