my_list = ['A','C','G','T','T','C','G','A','G']

print(my_list)
print()


for (n1, v1), (n2,v2) in zip(enumerate(my_list), itertools.islice(enumerate(my_list), 1, None)):
        print(v1)
        print(v2)
        print()

# gives me

['A', 'C', 'G', 'T', 'T', 'C', 'G', 'A', 'G']

(0, 'A')
(1, 'C')

(1, 'C')
(2, 'G')

(2, 'G')
(3, 'T')

(3, 'T')
(4, 'T')

(4, 'T')
(5, 'C')

(5, 'C')
(6, 'G')

(6, 'G')
(7, 'A')

(7, 'A')
(8, 'G')

(0, 'A')
(0, 'A')

(0, 'A')
(1, 'C')

.....
.....

(8, 'G')
(8, 'G')