def get_variant_id(variant_dict):
    """Build a variant id
    
        The variant id is a string made of CHROM_POS_REF_ALT
        
        The alt field for svs needs some massage to work downstream.
        
        Args:
            variant_dict (dict): A variant dictionary
        
        Returns:
            variant_id (str)
    """
    chrom = variant_dict['CHROM']
    pos = variant_dict['POS']
    ref = variant_dict['REF']
    #There are several symbols in structural variant calls that make
    #things hard. We will strip those symbols
    bad_chars = "<>[]:"
    alt = ''.join(c for c in variant_dict['ALT'] if c not in bad_chars)
    return '_'.join([chrom,pos,ref,alt])