def update_system_numbers(self):
scn_035_fields = record_get_field_instances(self.record, '<STR_LIT>')<EOL>new_fields = []<EOL>for field in scn_035_fields:<EOL><INDENT>subs = field_get_subfields(field)<EOL>if '<STR_LIT>' in subs:<EOL><INDENT>if subs['<STR_LIT>'][<NUM_LIT:0>].lower() == "<STR_LIT>" and subs.get('<STR_LIT:a>'):<EOL><INDENT>self.add_control_number("<STR_LIT>", subs.get('<STR_LIT:a>')[<NUM_LIT:0>])<EOL><DEDENT>if subs['<STR_LIT>'][<NUM_LIT:0>].lower() in ["<STR_LIT>", "<STR_LIT>", "<STR_LIT>", "<STR_LIT>", "<STR_LIT>"]:<EOL><INDENT>continue<EOL><DEDENT><DEDENT>new_fields.append(field_get_subfield_instances(field))<EOL><DEDENT>record_delete_fields(self.record, tag="<STR_LIT>")<EOL>for field in new_fields:<EOL><INDENT>record_add_field(self.record, tag="<STR_LIT>", subfields=field)<EOL><DEDENT>
035 Externals.