def claim(self, file_readers):
(prefix_to_readers,<EOL>filter_files,<EOL>unclaimed_set) = self._find_varscan_files(file_readers)<EOL>prefix_by_patients = self._split_prefix_by_patient(prefix_to_readers)<EOL>self._validate_vcf_readers(prefix_by_patients)<EOL>vcf_hc_pairs = self._pair_files(prefix_to_readers, filter_files)<EOL>self._validate_vcf_hc_pairs(vcf_hc_pairs)<EOL>vcf_readers = self._create_vcf_readers(vcf_hc_pairs)<EOL>return list(unclaimed_set), vcf_readers<EOL>
Recognizes and claims VarScan VCFs form the set of all input VCFs.

        Each defined caller has a chance to evaluate and claim all the incoming
        files as something that it can process. Since VarScan can claim
        high-confidence files as well, this process is significantly more
        complex than for other callers.

        Args:
            file_readers: the collection of currently unclaimed files

        Returns:
            A tuple of unclaimed readers and VarScanVcfReaders.