code: def update_pagenumber(self):
          
          for field in record_get_field_instances(self.record, '300'):
              for idx, (key, value) in enumerate(field[0]):
                  if key == 'a':
                      if "mult." not in value and value != " p":
                          field[0][idx] = ('a', re.sub(r'[^\d-]+', '', value))
                      else:
                          record_delete_field(self.record, '300',
                                              field_position_global=field[4])
                          break
docs: 300 page number.