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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 _cnvkit_by_type(items, background):
 """Dispatch to specific CNVkit functionality based on input type. """

    if len(items + background) == 1:
        return _run_cnvkit_single(items[0])
    elif vcfutils.get_paired_phenotype(items[0]):
        return _run_cnvkit_cancer(items, background)
    else:
        return _run_cnvkit_population(items, background)