想了下，理解题意的话是将字符串变为小写，那么不是字符串的是不是就应该保持不变呢

Discuss / Python / 想了下，理解题意的话是将字符串变为小写，那么不是字符串的是不是就应该保持不变呢

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#1 Created at ... [Delete] [Delete and Lock User]

#_*_ coding:utf-8 _*_

L1 = ['Hello', 'World', 18, 'Apple', None]

L2=[s.lower() for s in L1 if isinstance(s,str)]

L2

[40]:

['hello', 'world', 'apple']

[43]:

L2=[s.lower() if isinstance(s,str) else s for s in L1]

L2

[43]:

['hello', 'world', 18, 'apple', None]

#2 Created at ... [Delete] [Delete and Lock User]

L2 = [s.lower() for s in L1 if isinstance(s,str) else s]

这个为什么不行呢

#3 Created at ... [Delete] [Delete and Lock User]

同问

#4 Created at ... [Delete] [Delete and Lock User]

上面文章写了，在一个列表生成式中，for前面的if ... else是表达式，而for后面的if是过滤条件，不能带else。