Modify an existing signature

        Can modify the content, contenttype and name. An unset attribute will
        not delete the attribute but leave it untouched.
        :param: signature a zobject.Signature object, with modified
                         content/contentype/name, the id should be present and
                          valid, the name does not allows to identify the
                         signature for that operation.

def modify_signature(self, signature):
        """ Modify an existing signature

        Can modify the content, contenttype and name. An unset attribute will
        not delete the attribute but leave it untouched.
        :param: signature a zobject.Signature object, with modified
                         content/contentype/name, the id should be present and
                          valid, the name does not allows to identify the
                         signature for that operation.
        """
        # if no content is specified, just use a selector (id/name)
        dic = signature.to_creator(for_modify=True)

        self.request('ModifySignature', {'signature': dic})