def Check_SNP(vcf):
    """Checks whether input variant is a SNP and returns either 0 or 1

    Parameters
    ----------
    vcf : DataFrame
        vcf file with variants of interest

    Returns
    -------
    int
        an integer representation of whether or not a variant is a SNP
    """
    if ',' in vcf['ALT']:
        if len(vcf['REF']) == 1 and (len(vcf['ALT'].split(',')[0]) == 1 or 
            len(vcf['ALT'].split(',')[1]) == 1):
            return 1
        else:
            return 0
    elif len(vcf['REF']) == 1 and len(vcf['ALT']) == 1:
        return 1
    else:
        return 0
