def update_fields(self, updates):
for field in updates:<EOL><INDENT>if self._valid_field(field):<EOL><INDENT>self._track_changes.add(field)<EOL><DEDENT>else:<EOL><INDENT>raise ValueError('<STR_LIT>'.format(field))<EOL><DEDENT><DEDENT>if self.fields:<EOL><INDENT>self.fields.update(updates)<EOL><DEDENT>else:<EOL><INDENT>self.fields = updates<EOL><DEDENT>
Update the value for a field(s) in the listitem

:param update: A dict of {'field name': newvalue}