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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _strelka_variant_stats(variant, sample_info):
 """Parse a single sample"s variant calling statistics based on Strelka VCF output Parameters variant : varcode.Variant sample_info : dict Dictionary of Strelka-specific variant calling fields Returns ------- VariantStats """

    
    if variant.is_deletion or variant.is_insertion:
        # ref: https://sites.google.com/site/strelkasomaticvariantcaller/home/somatic-variant-output
        ref_depth = int(sample_info['TAR'][0]) # number of reads supporting ref allele (non-deletion)
        alt_depth = int(sample_info['TIR'][0]) # number of reads supporting alt allele (deletion)
        depth = ref_depth + alt_depth
    else:
        # Retrieve the Tier 1 counts from Strelka
        ref_depth = int(sample_info[variant.ref+"U"][0])
        alt_depth = int(sample_info[variant.alt+"U"][0])
        depth = alt_depth + ref_depth
    if depth > 0:
        vaf = float(alt_depth) / depth
    else:
        # unclear how to define vaf if no reads support variant
        # up to user to interpret this (hopefully filtered out in QC settings)
        vaf = None

    return VariantStats(depth=depth, alt_depth=alt_depth, variant_allele_frequency=vaf)