code: def release_port(upnp, external_port):
      
      mapping = upnp.getspecificportmapping(external_port, 'UDP')
  
      if mapping is None:
          log.error('could not find a port mapping', external=external_port)
          return False
      else:
          log.debug('found existing port mapping', mapping=mapping)
  
      if upnp.deleteportmapping(external_port, 'UDP'):
          log.info('successfully released port mapping', external=external_port)
          return True
  
      log.warning(
          'could not release port mapping, check your router for stale mappings',
      )
      return False
docs: Try to release the port mapping for `external_port`.
  
      Args:
          external_port (int): the port that was previously forwarded to.
  
      Returns:
          success (boolean): if the release was successful.