def read():
        """
        Read the process ID stored in this PID file.

        @return: The contained process ID.
        @rtype: L{int}

        @raise NoPIDFound: If this PID file does not exist.
        @raise EnvironmentError: If this PID file cannot be read.
        @raise ValueError: If this PID file's content is invalid.
        """

        Read the process ID stored in this PID file.

        @return: The contained process ID.
        @rtype: L{int}

        @raise NoPIDFound: If this PID file does not exist.
        @raise EnvironmentError: If this PID file cannot be read.
        @raise ValueError: If this PID file's content is invalid.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/application/runner/_pidfile.py