具有两个列表的嵌套列表理解 [英] Nested list comprehension with two lists

问题描述

我了解简单列表理解的工作原理，例如:

I understand how the simple list comprehension works eg.:

[x*2 for x in range(5)] # returns [0,2,4,6,8]

我也了解嵌套列表组合的工作原理:

and also I understand how the nested list comprehesion works:

w_list = ["i_have_a_doubt", "with_the","nested_lists_comprehensions"]

# returns the list of strings without underscore and capitalized
print [replaced.title() for replaced in [el.replace("_"," ")for el in w_list]]

所以，当我尝试这样做

l1 = [100,200,300]
l2 = [0,1,2]
[x + y for x in l2 for y in l1 ]

我期望这样:

[101,202,303]

但是我明白了:

[100,200,300,101,201,301,102,202,302]

所以我有一个更好的方法来解决问题，这给了我想要的东西

so I got a better way solve the problem, which gave me what I want

[x + y for x,y in zip(l1,l2)]

但是我不理解第一个代码中9个元素的返回

but I didn't understood the return of 9 elements on the first code

推荐答案

它有9个数字的原因是因为python对待

The reason it has 9 numbers is because python treats

[x + y for x in l2 for y in l1 ]

类似于

for x in l2:
    for y in l1:
       x + y

即，这是一个嵌套循环

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