Python socket 模块，SO_TYPE 实例源码

def is_socket(fd):
    """ Determine whether the file descriptor is a socket.

        :param fd: The file descriptor to interrogate.
        :return: ``True`` iff the file descriptor is a socket; otherwise
            ``False``.

        Query the socket type of `fd`. If there is no error, the file is a
        socket.

        """
    result = False

    file_socket = socket.fromfd(fd, socket.AF_INET, socket.SOCK_RAW)

    try:
        socket_type = file_socket.getsockopt(
            socket.SOL_SOCKET, socket.SO_TYPE)
    except socket.error as exc:
        exc_errno = exc.args[0]
        if exc_errno == errno.ENOTSOCK:
            # Socket operation on non-socket.
            pass
        else:
            # Some other socket error.
            result = True
    else:
        # No error getting socket type.
        result = True

    return result