def METHOD_NAME(self, property_sets):
    """Get the key schemas from secondary indexes"""
    keys = set()
    for properties, _ in property_sets:
        for index in properties:
            keys = keys.union(
                self._get_key_schema_attributes(
                    index.get_safe("KeySchema", list_node([], None, None), [], list)
                )
            )
    return keys