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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 _select_options(pat):
 """returns a list of keys matching `pat` if pat=="all", returns all registered options """


    # short-circuit for exact key
    if pat in _registered_options:
        return [pat]

    # else look through all of them
    keys = sorted(_registered_options.keys())
    if pat == 'all':  # reserved key
        return keys

    return [k for k in keys if re.search(pat, k, re.I)]