蟒蛇 a, b = b, a +b [英] Python a, b = b, a +b

问题描述

这是我的第一个问题，我开始学习 Python.是否有区别:

This is my first question and I started to learn Python. Is there a difference between:

a, b = b, a + b

和

a = b
b = a + b

当你在下面的例子中写它时，它显示了不同的结果.

When you write it in below example it shows different results.

def fib(n):
    a, b = 0, 1
    while a < n:
        print(a, end=' ')
        a, b = b, a + b
    print()
fib(1000)

和

def fib(n):
    a, b = 0, 1
    while a < n:
        print(a, end=' ')
        a = b
        b = a + b
    print()
fib(1000)

推荐答案

在 a, b = b, a + b 中，右边的表达式在赋值给左边之前先求值手边.所以等价于:

In a, b = b, a + b, the expressions on the right hand side are evaluated before being assigned to the left hand side. So it is equivalent to:

c = a + b
a = b
b = c

在第二个例子中，a 的值在 b = a + b 运行时已经改变了.因此，结果是不同的.

In the second example, the value of a has already been changed by the time b = a + b is run. Hence, the result is different.

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