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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_hetcaller(item):
 """Ensure upstream SV callers requires to heterogeneity analysis are available. """

    svs = _get_as_list(item, "svcaller")
    hets = _get_as_list(item, "hetcaller")
    if hets or any([x in svs for x in ["titancna", "purecn"]]):
        if not any([x in svs for x in ["cnvkit", "gatk-cnv"]]):
            raise ValueError("Heterogeneity caller used but need CNV calls. Add `gatk4-cnv` "
                             "or `cnvkit` to `svcaller` in sample: %s" % item["description"])