<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_variant_id(variant):
 """Get a variant id on the format chrom_pos_ref_alt"""

    variant_id = '_'.join([
            str(variant.CHROM),
            str(variant.POS),
            str(variant.REF),
            str(variant.ALT[0])
        ]
    )
    return variant_id