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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 calibrate_percentile_ranks(allele, predictor, peptides=None):
 """ Private helper function. """

    global GLOBAL_DATA
    if peptides is None:
        peptides = GLOBAL_DATA["calibration_peptides"]
    predictor.calibrate_percentile_ranks(
        peptides=peptides,
        alleles=[allele])
    return {
        allele: predictor.allele_to_percent_rank_transform[allele],
    }