seq1 = 'ATGTCAGATCGG'
seq2 = 'TCGATCGATTGTTTAACTGAGGGGGCT'

print 'first codon seq1:', seq1[0:3], 'last codon seq1:', seq1[-3:] #[-3:] grabs the last 3 characters at the end length of the string
print 'first codon seq2:', seq2[0:3],  'last codon seq2:', seq2[-3:]