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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 _reads_in_peaks(bam_file, peaks_file, sample):
 """Calculate number of reads in peaks"""

    if not peaks_file:
        return {}
    rip = number_of_mapped_reads(sample, bam_file, bed_file = peaks_file)
    return {"metrics": {"RiP": rip}}