def popCommandQueue(self):
        """
        Return the front element of the command queue, or None if empty.
        """
        if self.actionQueue:
            return self.actionQueue.pop(0)
        else:
            return None

        Return the front element of the command queue, or None if empty.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/protocols/ftp.py