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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 generate_sub_codons_left(codons_dict):
 """Generate the sub_codons_left dictionary of codon prefixes. Parameters codons_dict : dict Dictionary, keyed by the allowed 'amino acid' symbols with the values being lists of codons corresponding to the symbol. Returns ------- sub_codons_left : dict Dictionary of the 1 and 2 nucleotide prefixes (read from 5') for each codon in an 'amino acid' grouping """

    sub_codons_left = {}
    for aa in codons_dict.keys():
        sub_codons_left[aa] = list(set([x[0] for x in codons_dict[aa]] + [x[:2] for x in codons_dict[aa]]))
        
    return sub_codons_left