Python:变量的用法及其差异("a，b = 0，1" VS"a = 0"，"b = 1") [英] Python: Usage of Variables and their difference ("a, b = 0, 1" VS "a = 0", "b = 1")

问题描述

我正在查看Python手册，并找到了斐波那契数生成器的以下代码段:

I was looking at the Python Manual and found this snippet for a Fibonacci-Number generator:

def fib(n):    # write Fibonacci series up to n
    a, b = 0, 1
    while b < n:
        print(b, end=' ')
        a, b = b, a+b
    print()

输出取决于n并返回有效的斐波那契数列.

The output is dependent on n and returns a valid Fibonacci sequence.

如果您将其重塑为像这样分别使用变量"a"和"b":

If you remodel this to use the variables "a" and "b" seperately like so:

def fib(n):    # write Fibonacci series up to n
    a = 0
    b = 1
    while b < n:
        print(b, end=' ')
        a = b
        b = a+b
    print()

然后它将打印一个以2的幂递增的数字序列(例如1、2、4、8、16等).

then it will print a number sequence that increments by the power of 2 (e.g. 1, 2, 4, 8, 16 and so on).

所以我想知道为什么会这样吗?两次使用变量之间的实际区别是什么?

So I was wondering why that happens? What is the actual difference between the two uses of variables?

推荐答案

操作:

a，b = b，a + b

等效于:

temp = a
a = b
b += temp

它使您可以同时进行两个计算，而无需中间/临时变量.

It lets you simultaneously do two calculations without the need of an intermediate/temporary variable.

区别在于，在第二段代码中，当您执行第二行 b = a + b 时，您已经在上一行中修改了 a 与第一段代码不同.

The difference is that in your second piece of code, when you do the second line b = a+b, you have already modifed a in the previous line which is not the same as the first piece of code.

>>> a = 2
>>> b = 3
>>> a,b
2 3
>>> a,b = b,a
>>> a,b
3 2

另一方面，如果您使用问题中显示的第二种方法:

On the other hand, if you use the second approach shown in your question:

>>> a = 2
>>> b = 3
>>> a,b
2 3
>>> a = b
>>> b = a
>>> a,b
3 3

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