了解Python 3列出了每个元素的无打印值 [英] Understanding Python 3 lists printing None value for each element

问题描述

作为一个非常精通Python的菜鸟，我正在打印版本3中的列表的所有元素，经过全面研究后，我找不到这种行为的解释.

As a very noob with in Python I'm printing all elements of a list in version 3, and after a comprehensive research I couldn't find an explanation for this kind of behavior.

但是，我知道每个函数都必须返回一些值，当未定义该函数时，该函数将返回"Null"(在Python中为"None").但是，为什么在这种情况下，正确打印所有元素后，它会为另一个列表中的每个元素打印无"?

However, I know every function must return some value and when it's not defined the function returns "Null" (or "None" in Python). But why in this case, after printing all elements correctly it prints "None" for each element in another list?

>>> a_list = [1,2]
>>> a_list
[1, 2]
>>> [print(f) for f in a_list]
1
2
[None, None]

推荐答案

None是print函数的返回值.

当您指的是for f in a_list: print(f)时，请勿使用[print(f) for f in a_list].

Don't use [print(f) for f in a_list] when you mean for f in a_list: print(f).

这篇关于了解Python 3列出了每个元素的无打印值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！