列表理解返回值加上 [None, None, None]，为什么? [英] List comprehension returning values plus [None, None, None], why?

问题描述

我正在学习理解.我得到了 print(x) 部分(我认为.它打印了通过in"测试的 x 的值)但为什么它之后还返回一个 None 列表?

<预><代码>>>>G['a', 'x', 'p']>>>[print(x) for x in g]一种X磷[无，无，无]#这是什么?

解决方案

您使用列表推导式打印列表中的项目，然后打印列表本身.尝试将列表分配给变量.

<预><代码>>>>G['a', 'x', 'p']>>>x = [print(x) for x in g]一种X磷#

现在列表在 x 中并且没有打印.名单还在……

<预><代码>>>>打印(x)[无，无，无]>>>X[无，无，无]

Im studying comprehensions. I get the print(x) part (i think. It prints the value of x that passes the 'in' test) but why is it also returning a list of None afterward?

>>> g
['a', 'x', 'p']

>>> [print(x) for x in g]
a
x
p
[None, None, None] #whats this? 

解决方案

You use a list comprehension to print the items in the list, and then the list itself is printed. Try assigning the list to a variable instead.

>>> g
['a', 'x', 'p']

>>> x = [print(x) for x in g]
a
x
p
#

Now the list is in x and isnt printed. The list is still there...

>>> print(x)
[None, None, None]
>>> x
[None, None, None]

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