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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