Python之旅——“a = a + b b = a - b “ VS “a, b = a + b, a - b“

 

a.  二者输出结果肯定不相同。

b. 第一个利用C/C++的思维进行思考即可；第二个是利用python中的元组打包和序列解包的思维思考。

 

假设a为10，b为8，示例解析：

a.  a = a + b  b = a - b

a = 10
b = 8

print("Add first")
a = a + b #a = 10 + 8
print("a = ", a)
b = a - b #b = 18 - 8
print("b = ", b)

print()

a = 10
b = 8
print("Minus first")
b = a - b #b = 10 - 8
print("b = ", b)
a = a + b #a = 10 + 2
print("a = ", a)

print()

 

输出结果：

Add first
a = 18
b = 10

Minus first
b = 2
a = 12

 

b. a, b = a + b, a - b

    该等式是先将等号右边的计算结果先打包成一个临时元组，然后将该临时元组进行列表解包，分别赋值给a和b。

a = 10
b = 8
print("Add first")
result = a + b, a - b
a, b = a + b, a - b
print("a = ", a, " b = ", b)
print("result:", result)
print()

a = 10
b = 8
print("Minus first")
result = a - b, a + b
a, b = a - b, a + b
print("a = ", a, " b = ", b)
print("result:", result)
print()

输出结果：

Add first
a = 18 b = 2
result: (18, 2)

Minus first
a = 2 b = 18
result: (2, 18)