在Python中明智地串联两个Strings元素列表，而没有嵌套的for循环 [英] Concatenating two lists of Strings element wise in Python without Nested for loops

问题描述

我有两个字符串列表: ls1 = ['a'，'b'，'c'，'d'] 和 ls2 = ['k'，'j'，'l'，'m']

I have two lists of strings: ls1 = ['a','b','c','d'] and ls2 = ['k','j','l','m']

我想创建第三个列表: ls3 = ['a-k'，'a-j'，'a-l'，'a-m'，'b-k'，'b-j'，'b-l'，'b-m'...'d-m'] ，其中包含16个元素.

I want to create a 3rd list: ls3 = ['a-k','a-j','a-l','a-m','b-k','b-j','b-l','b-m'...'d-m'] which has 16 elements.

我可以使用以下嵌套的 for 循环

I can achieve this quite easily with the following nested for loops

ls3 = [] 
for elem in ls1:
    for item in ls2:
        ls3.append(elem+'-'+item)

但是，这不是Python风格，它揭示了我的C代码背景.

However, this isn't very Pythonic and reveals my C-code background.

我尝试了使用 map 和 lambda 的更加Pythonic的解决方案:

I attempted a more Pythonic solution with map and lambda:

[ map(lambda x,y: x+'-'+y, a,b) for a,b in zip(ls1,ls2) ]

但是我真的不知道我在做什么.

But I don't really know what I'm doing yet.

通过嵌套的 for 循环可以完成我的工作的Python方法是什么?

What is a Pythonic way to achieve what I've done with my nested for loops?

推荐答案

您所使用的技术完全是Python风格的，并且在将列表理解引入语言之前，它还是属于规范的.但是，您建议使用 zip 的那个将不起作用，因为您希望使用 ls1 和 ls2 中的所有成对元素，但要使用> zip 只是使用相应的元素而不是所有组合来创建对.

The technique you have used is perfectly Pythonic, and until list comprehensions were introduced into the language would have been canonical. The one you suggest using zip, however, won't work, because you want all pairs of elements from ls1 and ls2, but zip simply creates pairs using the corresponding elements rather than all combinations.

如果您想使用更紧凑的代码，则应该使用适当的列表理解

If you'd like to use more compact code then the appropriate list comprehension would be

ls3 = [x+'-'+y for x in ls1 for y in ls2]

对于大型列表，或者在需要每盎司性能的情况下(这永远不是您的首要考虑)，请参阅@PaulPanzer的答案，他解释了一种更高效但稍微复杂的技术.

For large lists, or where you need every ounce of performance (which should never be your first consideration) see the answer from @PaulPanzer, who explains a more efficient though slightly more complex technique.

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