import binascii


def as_hex(bs: bytes) -> str:
    """
    Convert the bytes ``bs`` to a ``"ab 12 cd 34"`` string. ::

        >>> as_hex(bytes([1, 2, 3]))
        '01 02 03'
    """
    if not bs:
        return "<none>"
    hx = binascii.hexlify(bs).decode("ascii")
    return " ".join(["".join(s) for s in zip(hx[::2], hx[1::2])])