When we combine prefix + alt + suffix into a single string,
        what are is base-0 index interval which gets us back the alt
        sequence? First returned index is inclusive, the second is exclusive.

def variant_indices(self):
        """
        When we combine prefix + alt + suffix into a single string,
        what are is base-0 index interval which gets us back the alt
        sequence? First returned index is inclusive, the second is exclusive.
        """
        variant_start_index = len(self.prefix)
        variant_len = len(self.alt)
        variant_end_index = variant_start_index + variant_len
        return variant_start_index, variant_end_index