Iterate over variants in a region.

def get_variants_in_region(self, chrom, start, end):
        """Iterate over variants in a region."""
        bim = self.bim.loc[
            (self.bim["chrom"] == CHROM_STR_TO_INT[chrom]) &
            (start <= self.bim["pos"]) &
            (self.bim["pos"] <= end)
        ]
        for i, g in enumerate(self.bed.iter_geno_marker(bim.index)):
            info = bim.iloc[i, :]
            name, geno = g
            yield Genotypes(
                Variant(info.name, CHROM_INT_TO_STR[info.chrom],
                        info.pos, [info.a1, info.a2]),
                self._normalize_missing(geno),
                reference=info.a2,
                coded=info.a1,
                multiallelic=info.multiallelic
            )