1.字符串下标

# 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