Exercise 1 solution

def reverse_complement(s):
    return s.translate(str.maketrans("ACGT", "TGCA"))[::-1]

for s in ("ATGC", "GGGATTT", "AAAACCCGGT"):
    rc = reverse_complement(s)
    print(s, rc, reverse_complement(rc) == s)
print(reverse_complement("GAATTC") == "GAATTC")
print(reverse_complement("GGATCC") == "GGATCC")

Output:

ATGC GCAT True
GGGATTT AAATCCC True
AAAACCCGGT ACCGGGTTTT True
True
True

Reading it: applying the function twice always returns the original, because complementing and reversing each undo themselves. GAATTC and GGATCC are palindromic in this sense: they read the same as their own reverse complement. (Short sequences like these are often cut by enzymes used in the laboratory; check before relying on that.)