def host_and_port(host_or_port):
    """
    Return full hostname/IP + port, possible input formats are:
      * host:port  -> host:port
      * :          -> localhost:4200
      * :port      -> localhost:port
      * host       -> host:4200
    """
    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'