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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def render_flags(flags, bit_list):
 """Show bit names. """

    res = []
    known = 0
    for bit in bit_list:
        known = known | bit[0]
        if flags & bit[0]:
            res.append(bit[1])
    unknown = flags & ~known
    n = 0
    while unknown:
        if unknown & 1:
            res.append("UNK_%04x" % (1 << n))
        unknown = unknown >> 1
        n += 1

    if not res:
        return '-'

    return ",".join(res)