code: def tracking_number(self, service: str = 'usps') -> str:
          
          service = service.lower()
  
          if service not in ('usps', 'fedex', 'ups'):
              raise ValueError('Unsupported post service')
  
          services = {
              'usps': (
                  '#### #### #### #### ####',
                  '@@ ### ### ### US',
              ),
              'fedex': (
                  '#### #### ####',
                  '#### #### #### ###',
              ),
              'ups': (
                  '1Z@####@##########',
              ),
          }
          mask = self.random.choice(services[service])  # type: ignore
          return self.random.custom_code(mask=mask)
docs: Generate random tracking number.
  
          Supported services: USPS, FedEx and UPS.
  
          :param str service: Post service.
          :return: Tracking number.