<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_previous_assessment_section(self, assessment_section_id):
 """Gets the previous section before section_id. Assumes that section list exists in taken and section_id is in section list. Assumes that Section parts only exist as children of Assessments """

        if self._my_map['sections'][0] == str(assessment_section_id):
            raise errors.IllegalState('already at the first section')
        else:
            return self._get_assessment_section(
                Id(self._my_map['sections'][self._my_map['sections'].index(str(assessment_section_id)) - 1]))