# 字符串下标[起始位置 : 终止位置 : 间隔 :]
say = "0123456789"
print(say[5]) # 5
print(say[-2]) # 8
print(say[2:5]) # 234
print(say[:5]) # 01234
print(say[5:]) # 56789
print(say[::3]) # 0369
print(say[1:8:3]) # 147
print(say[::-1]) # 9876543210
print(say[-5:]) # 56789
print(say[-5:-2]) # 567
