lambda和python中的过滤器 [英] lambda and filter in python

问题描述

我有以下字符串，我想通过过滤X来解码

I have the following string and I wanna decode by filtering the X's

garbled = "IXXX aXXmX aXXXnXoXXXXXtXhXeXXXXrX sXXXXeXcXXXrXeXt mXXeXsXXXsXaXXXXXXgXeX!XX"

我想过滤.我尝试了以下代码

And I would like to filter. I tried the following code

message = filter(lambda x: garbled.remove(x) if x == "X", garbled)

我没有通过这种方式工作.我找到了其他解决方案:

I did not make this way work. I have found this other solution:

message = filter(lambda x: x != "X", garbled)

但是我仍然想知道为什么第一个不起作用.我可以解决它吗?

But I still wonder why did not work the first one. Can I fix it?

(我是python btw的新手)，谢谢！

(I am new in python btw) thanks!

推荐答案

filter(function, iterable)执行以下过程:

1. 一次浏览一次iterable中的元素(即第二个参数).
2. 对于每个元素，请对该元素调用function(即第二个参数)，看看它是否返回true.
3. 仅将function返回true的那些元素收集在一起，并返回这些元素的新列表.

1. Go through the elements in iterable (i.e. the second parameter) one at a time.
2. For each one of those elements, call function (i.e. the second parameter) on that element and see whether it returns true.
3. Collect together only those elements where the function returned true, and return a new list of those.

看看如果您为function参数传递lambda x: garbled.remove(x) if x == "X"会在步骤2中发生什么:filter()对自己说:嗯，如果我设置了x="I"，那么garbled.remove(x) if x == "X"是真的吗?".就像您在filter()的第二个参数中大喊大叫:嘿，请删除所有"X" s".但这并不是去那里的正确选择.要求非常精确:它必须是一个接受元素并返回true或false值的函数.

Look at what happens in step 2 if you pass lambda x: garbled.remove(x) if x == "X" for the function parameter: filter() says to itself, "Hmm, if I set x="I" then is garbled.remove(x) if x == "X" true?". It's like you're shouting an instruction at filter() in its second parameter: "hey, please remove all the "X"s". But that's just not the right thing to go there. The requirements are very precise: it must be a function that takes an element and returns a true or false value.

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