code: def network(prefix, default_length=24):
      
      address, pfxlen = parse_prefix(prefix, default_length)
      ip = ip2int(address)
      return int2ip(ip & pfxlen2mask_int(pfxlen))
docs: Given a prefix, this function returns the corresponding network
      address.
  
      :type  prefix: string
      :param prefix: An IP prefix.
      :type  default_length: long
      :param default_length: The default ip prefix length.
      :rtype:  string
      :return: The IP network address.