def _get_assessment_part(self, part_id=None):
if part_id is None:<EOL><INDENT>return self._assessment_part<EOL><DEDENT>if part_id not in self._assessment_parts:<EOL><INDENT>lookup_session = self._get_assessment_part_lookup_session()<EOL>self._assessment_parts[part_id] = lookup_session.get_assessment_part(part_id)<EOL><DEDENT>return self._assessment_parts[part_id]<EOL>
Gets an AssessmentPart given a part_id.

        Returns this Section's own part if part_id is None.

        Make this a private part, so that it doesn't collide with the AssessmentPart.get_assessment_part
        method, which does not expect any arguments...