libnum.n2s也有相同的效果，打字也更方便

long_to_bytes(n, blocksize=0)

        正整数转化为byte类型字符串

    Convert a positive integer to a byte string using big endian encoding.

    If :data:`blocksize` is absent or zero, the byte string will
    be of minimal length.

    Otherwise, the length of the byte string is guaranteed to be a multiple
    of :data:`blocksize`. If necessary, zeroes (``\x00``) are added at the left.

    .. note::
        In Python 3, if you are sure that :data:`n` can fit into
        :data:`blocksize` bytes, you can simply use the native method instead::

            >>> n.to_bytes(blocksize, 'big')

        For instance::

            >>> n = 80
            >>> n.to_bytes(2, 'big')
            b'\x00P'

        However, and unlike this ``long_to_bytes()`` function,
        an ``OverflowError`` exception is raised if :data:`n` does not fit.