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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 complete_pool_members(arg):
 """ Complete member prefixes of pool """

    # pool should already be globally set
    res = []
    for member in Prefix.list({ 'pool_id': pool.id }):
        res.append(member.prefix)

    return _complete_string(arg, res)