带有if但不包含else的Python lambda [英] Python lambda with if but without else

问题描述

我正在编写一些lambda函数，无法弄清楚.有没有办法在python中有类似lambda x: x if (x<3)的东西?由于lambda a,b: a if (a > b) else b可以正常工作.到目前为止，lambda x: x < 3 and x or None似乎是我找到的最接近的东西.

I was writing some lambda functions and couldn't figure this out. Is there a way to have something like lambda x: x if (x<3) in python? As lambda a,b: a if (a > b) else b works ok. So far lambda x: x < 3 and x or None seems to be the closest i have found.

推荐答案

lambda与任何函数一样，必须具有返回值.

A lambda, like any function, must have a return value.

lambda x: x if (x<3)不起作用，因为它没有指定如果不是x<3会返回的内容.默认情况下，函数返回None，所以您可以这样做

lambda x: x if (x<3) does not work because it does not specify what to return if not x<3. By default functions return None, so you could do

lambda x: x if (x<3) else None

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但是也许您正在寻找的是具有if条件的列表理解.例如:

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But perhaps what you are looking for is a list comprehension with an if condition. For example:

In [21]: data = [1, 2, 5, 10, -1]

In [22]: [x for x in data if x < 3]
Out[22]: [1, 2, -1]

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