code: def host_and_port(host_or_port):
      
      if ':' in host_or_port:
          if len(host_or_port) == 1:
              return 'localhost:4200'
          elif host_or_port.startswith(':'):
              return 'localhost' + host_or_port
          return host_or_port
      return host_or_port + ':4200'
docs: Return full hostname/IP + port, possible input formats are:
        * host:port  -> host:port
        * :          -> localhost:4200
        * :port      -> localhost:port
        * host       -> host:4200