for letter in ['A', 'B', 'C']: print(letter) # 출력값 A B C
for letter in enumerate(['A', 'B', 'C']): print(letter) #출력값 (0, 'A') (1, 'B') (2, 'C')
for idx, letter in enumerate(['A', 'B', 'C']): print(idx, letter) #출력값 0 A 1 B 2 C