only.py

#!/usr/bin/env python
# coding: utf-8

import socket
import functools


def nop():
    """no operation"""


class only(object):
    def __init__(self, socket_name='', on_error=nop):
        self.socket_name = socket_name
        self.error = on_error

    def __call__(self, f): 
        @functools.wraps(f)
        def _wrap(*args, **kwargs):
            s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
            try:
                s.bind(self.socket_name)
                result = f(*args, **kwargs)
            except socket.error:
                result = self.error()

            finally:
                s.close()

            return result

        return _wrap