from collections import Counter


def contacodon(seq):
    stops = ["TAA", "TAG", "TGA"]
    count = Counter()
    for i in range(seq.find('ATG'), len(seq) + 1, 3):
        codon = seq[i: i + 3]
        count.update([codon])
        if codon in stops:
            break
    return dict(count)


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