'(typ, [data, ...]) = fetch(message_set, message_parts)
Fetch (parts of) messages.
\'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,
followed by a string containing the trailer.'

def fetch(self, message_set, message_parts, **kw):

    name = 'FETCH'
    kw['untagged_response'] = name
    return self._simple_command(name, message_set, message_parts, **kw)
