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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 _read_truth_freqs(in_file):
 """Read frequency of calls from truth VCF. Currently handles DREAM data, needs generalization for other datasets. """

    out = {}
    with VariantFile(in_file) as bcf_in:
        for rec in bcf_in:
            freq = float(rec.info.get("VAF", 1.0))
            out[_get_key(rec)] = freq
    return out