@classmethod
def from_str(cls, s, rs=None):
    """Parses a variant object from a str of the form chrXX:YYYY_R/A.

        :param s: The string to parse the SNP from (Format: chrXX:YYY_R/A).
        :param rs: An optional parameter specifying the rs number.

        :returns: A list of SNP objects.

        If it is a multi-allelic loci, the list will contain one SNP per
        alternative allele.

        If it is not, this will be a list of length 1...

        """
    s = s.lstrip('chr')
    chrom, s = s.split(':')
    pos, s = s.split('_')
    alleles = s.split('/')
    ref = alleles[0]
    alts = list(alleles[1:])
    var_list = []
    for alt in alts:
        v = cls(chrom, pos, rs, ref, alt)
        var_list.append(v)
    return var_list
