def contacodon(seq):
    # Lista de stop codons:
    stops = ["TAA", "TAG", "TGA"]

    count = {}
    for i in range(seq.find('ATG'), len(seq) + 1, 3):
        codon = seq[i: i + 3]
        if codon in count:
            count[codon] += 1
        else:
            count[codon] = 1

        # Se tiver encontrado um stop codon, pare de iterar:
        if codon in stops:
            break
    return count


seq = "GCGATCGAGATGAGCATCGCATCGCGGACTACCGCGCGCGCGCGCGGGAGATGAGCATCGACGACTCGACTAG"
print(contacodon(seq))