code: def passport_series(self, year: int = None) -> str:
          
          if not year:
              year = self.random.randint(10, 18)
  
          region = self.random.randint(1, 99)
          return '{:02d} {}'.format(region, year)
docs: Generate random series of passport.
  
          :param year: Year of manufacture.
          :type year: int or None
          :return: Series.
  
          :Example:
              02 15.