带有两个列表的嵌套列表理解

Nested list comprehension with two lists(带有两个列表的嵌套列表理解)

问题描述

我了解简单列表推导式的工作原理，例如:

I understand how the simple list comprehension works eg.:

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

而且我也理解嵌套列表解析的工作原理:

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，当我尝试这样做时

so, when I tried do this

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

我预料到了:

[100,201,302]

但我得到了这个:

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

所以我找到了解决问题的更好方法，这给了我想要的

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

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

但是我没看懂第一个代码的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

之所以有9个数字是因为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，它是一个嵌套循环

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