Iterate over variants in a region.

def get_variants_in_region(self, chrom, start, end):
        """Iterate over variants in a region."""
        region = self.get_vcf()(
            "{}:{}-{}".format(chrom, start, end)
        )
        for v in region:
            for coded_allele, g in self._make_genotypes(v.ALT, v.genotypes):
                variant = Variant(
                    v.ID, v.CHROM, v.POS, [v.REF, coded_allele]
                )
                yield Genotypes(variant, g, v.REF, coded_allele,
                                multiallelic=len(v.ALT) > 1)