'Fetch (parts of) messages.
(typ, [data, ...]) = <instance>.fetch(message_set, message_parts)
\'message_parts\' should be a string of selected parts
enclosed in parentheses, eg: "(UID BODY[TEXT])".
\'data\' are tuples of message part envelope and data.'

def fetch(self, message_set, message_parts):

    name = 'FETCH'
    (typ, dat) = self._simple_command(name, message_set, message_parts)
    return self._untagged_response(typ, dat, name)
