列表理解中的函数-是否多次评估 [英] function inside list comprehension - is it evaluated multiple times

问题描述

哪个是在python中进行列表理解的更好方法(就计算时间和cpu周期而言). 在示例(1)中，值f(r)是在每次迭代中求值还是仅求值一次并缓存?

Which one's a better way of doing list comprehension in python (in terms of computation time & cpu cycles). In example (1) is the value f(r) evaluated in each iteration or is it evaluated once and cached ?

1. y = [x*f(r) for x in xlist]

c = f(r)

y = [x*c for x in xlist]

其中

def f(r):
    ... some arbitrary function ...

推荐答案

我可能会选择后者，因为Python编译器不知道该函数是否具有副作用，因此会为每个元素调用该函数.

I would probably choose the latter because the Python compiler doesn't know if the function has side-effects so it is called for each element.

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