def release(self):
        """
        Release the lock.  If there is a waiting list, then the first
        L{Deferred} in that waiting list will be called back.

        Should be called by whomever did the L{acquire}() when the shared
        resource is free.
        """
        assert self.locked, "Tried to release an unlocked lock"
        self.locked = False
        if self.waiting:
            # someone is waiting to acquire lock
            self.locked = True
            d = self.waiting.pop(0)
            d.callback(self)

        Release the lock.  If there is a waiting list, then the first
        L{Deferred} in that waiting list will be called back.

        Should be called by whomever did the L{acquire}() when the shared
        resource is free.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/defer.py