def __init__(self, parent=None):
self.attributes = None<EOL>self._parent = parent<EOL>if self._parent:<EOL><INDENT>self._parent = weakref.ref(parent)<EOL><DEDENT>if not self.__class__ == XMLSchemaComponentand not (type(self.__class__.required) == type(XMLSchemaComponent.required)and type(self.__class__.attributes) == type(XMLSchemaComponent.attributes)and type(self.__class__.contents) == type(XMLSchemaComponent.contents)):<EOL><INDENT>raise RuntimeError('<STR_LIT>' %self.__class__)<EOL><DEDENT>
parent -- parent instance
           instance variables:
               attributes -- dictionary of node's attributes