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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 best_precursor(clus, loci):
 """ Select best precursor asuming size around 100 nt """

    data_loci = sort_precursor(clus, loci)
    current_size = data_loci[0][5]
    best = 0
    for item, locus in enumerate(data_loci):
        if locus[3] - locus[2] > 70:
            if locus[5] > current_size * 0.8:
                best = item
                break
    best_loci = data_loci[best]
    del data_loci[best]
    data_loci.insert(0, best_loci)
    return data_loci