def getSubPart(part):
        """
        Retrieve a MIME sub-message

        @type part: L{int}
        @param part: The number of the part to retrieve, indexed from 0.

        @raise IndexError: Raised if the specified part does not exist.
        @raise TypeError: Raised if this message is not multipart.

        @rtype: Any object implementing L{IMessageIMAPPart}.
        @return: The specified sub-part.
        """

        Retrieve a MIME sub-message

        @type part: L{int}
        @param part: The number of the part to retrieve, indexed from 0.

        @raise IndexError: Raised if the specified part does not exist.
        @raise TypeError: Raised if this message is not multipart.

        @rtype: Any object implementing L{IMessageIMAPPart}.
        @return: The specified sub-part.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/interfaces.py