def _init_properties(self):
self._missing = {}<EOL>for k, p in self.params.items():<EOL><INDENT>if p.required:<EOL><INDENT>self._missing[k] = p<EOL><DEDENT>if isinstance(p, Derived):<EOL><INDENT>if p.loader is None:<EOL><INDENT>p.loader = self.__getattribute__("<STR_LIT>" % k)<EOL><DEDENT>elif isinstance(p.loader, str):<EOL><INDENT>p.loader = self.__getattribute__(p.loader)<EOL><DEDENT><DEDENT><DEDENT>
Loop through the list of Properties,
        extract the derived and required properties and do the
        appropriate book-keeping