Squid3 trying to add a custom external_acl_type

I'm trying to create an external acl helper for squid3 to (hopefully) cut down some config lines from my squid3 server and I wrote a simple python script for it:

#!/usr/bin/python

import sys
import logging
import time


logger = logging.getLogger( 'squid_auth' )
logger.setLevel( logging.DEBUG )
fh = logging.FileHandler( 'spam.log' )
fh.setLevel( logging.DEBUG )
formatter = logging.Formatter( '%(asctime)s - %(name)s - %(levelname)s - %(message)s' )
fh.setFormatter( formatter )
logger.addHandler( fh )


def grant ():
      sys.stdout.write( 'OK\n' )
      sys.stdout.flush()


def deny ():
      sys.stdout.write( 'ERR\n' )
      sys.stdout.flush()


while True:
      line = sys.stdin.readline().strip()
      if line:
              logger.info( line )
              grant()
      else:
              time.sleep( 1 )

and added it into my squid.conf:

external_acl_type custom_acl %SRC %LOGIN %DST /etc/changemyip/squid/config/acl.py
acl CustomAcl external custom_acl
http_access allow CustomAcl

The path to the script is right (I can execute it in shell), the program has execute rights and everything but, when I reload squid I get this error about 5-6 times then squid crashes:

Aug 17 14:08:52 server7 (squid): The custom_acl helpers are crashing too rapidly, need help!
Aug 17 14:08:52 server7 squid[28233]: Squid Parent: child process 28290 exited with status 1
Aug 17 14:08:52 server7 squid[28233]: Exiting due to repeated, frequent failures

As you can see the script is just printing OK\n to the stdout to grant everyone. I haven't even started implementing any logic to it.

Tested with squid version: 3.1.19