Return a specific variant.

            Args:
                case_id (str): Path to vcf file
                variant_id (str): A variant id

            Returns:
                variant (Variant): The variant object for the given id

def variant(self, case_id, variant_id):
        """Return a specific variant.

            Args:
                case_id (str): Path to vcf file
                variant_id (str): A variant id

            Returns:
                variant (Variant): The variant object for the given id
        """
        case_obj = self.case(case_id=case_id)
        vcf_file_path = case_obj.variant_source
        self.head = get_header(vcf_file_path)

        self.vep_header = self.head.vep_columns
        self.snpeff_header = self.head.snpeff_columns

        handle = VCF(vcf_file_path)

        for index, variant in enumerate(handle):
            index += 1
            line_id = get_variant_id(variant_line=str(variant)).lstrip('chrCHR')
            if line_id == variant_id:
                return self._format_variants(
                    variant=variant,
                    index=index,
                    case_obj=case_obj,
                    add_all_info=True
                    )

        return None