python中的all()如何处理空列表 [英] How does all() in python work on empty lists

问题描述

我指的是下面的python代码

I am referring to the following python code

all(a==2 for a in my_list)

如果 my_list 中的所有元素都是 2，我希望上面的代码返回 True.但是当我将 my_list 设为空并将其作为

I expect the above code to return True if all the elements in my_list are 2. but when I make my_list empty and run it as

my_list = []
all(a==2 for a in my_list) 

它也返回True.我对这种行为感到困惑.是否不应该返回 False，因为 my_list 中没有值为 2 的元素?

it returns True as well. I am confused with this behaviour. Is it not supposed to return False as there is no element in my_list with value 2?

推荐答案

这是真的，因为对于列表中的每个元素，它们都是 0，它们都等于 2.

It's true because for every element in the list, all 0 of them, they all are equal to 2.

你可以认为 all 被实现为:

You can think of all being implemented as:

def all(list, condition):
  for a in list:
    if not condition(a):
      return false
  return true

而 any 是:

def any(list, condition):
  for a in list:
    if condition(a):
      return true
  return false

也就是说，all在被证明有罪之前都是无罪的，而any在被证明无罪之前都是有罪的.

That is to say, all is innocent until proven guilty, and any is guilty until proven innocent.

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