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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 _check_aligner(item):
 """Ensure specified aligner is valid choice. """

    allowed = set(list(alignment.TOOLS.keys()) + [None, False])
    if item["algorithm"].get("aligner") not in allowed:
        raise ValueError("Unexpected algorithm 'aligner' parameter: %s\n"
                         "Supported options: %s\n" %
                         (item["algorithm"].get("aligner"), sorted(list(allowed))))