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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 alleles_to_retrieve(df):
 """Alleles to retrieve from genome fasta Get a dict of the genome fasta contig title to a list of blastn results of the allele sequences that must be retrieved from the genome contig. Args: df (pandas.DataFrame):
 blastn results dataframe Returns: {str:[pandas.Series]}: dict of contig title (header name) to list of top blastn result records for each marker for which the allele sequence must be retrieved from the original sequence. """

    contig_blastn_records = defaultdict(list)
    markers = df.marker.unique()
    for m in markers:
        dfsub = df[df.marker == m]
        for i, r in dfsub.iterrows():
            if r.coverage < 1.0:
                contig_blastn_records[r.stitle].append(r)
            break
    return contig_blastn_records