交换数字

a = 6 
b = 9
# 将a,b数字交换
# 解法一:
# 借用临时变量
c = b
b = a
a = c

# 解法二:
a = a + b
a = a - b
b = a - b 

# 解法三:
# python 特有
a, b = b, a  # 以b, a 是一个元组的形式,小括号省略没写