How to achieve a huge number of for loop in python?

Asked Aug 15 '16 at 09:24

Active Aug 15 '16 at 09:40

Viewed 60 times

I would like to write a program to get every sum from a list. For example:

L = [['7'], ['3', '8'], ['8', '1', '0']]

I would like to get:

8 + 3 + 7

8 + 8 + 7

1 + 3 + 7

1 + 8 + 7

0 + 3 + 7

0 + 8 + 7

So, I wrote my program in this way:

 for x1 in L[-1]:
     for x2 in L[-2]:
         for x3 in L[-3]:
             print (int(x1) + int(x2) + int(x3))

However, there may be a huge number lists. In this way, I have to write a huge number of for loop. Is there any other way that I can use to write my program?

itertools.product works well for this question, but is there any way to do not import anything to solve this question?

edited Aug 15 '16 at 09:35

asked Aug 15 '16 at 09:24

Mangosteen

Why don't you want to use `itertools`? – Chris_Rands Aug 15 '16 at 09:41
@Chris_Rands Because this is a practice and we are not allowed to import extra packages. – Mangosteen Aug 15 '16 at 09:48
If `itertools.product` can not be used, `reduce` is a good choice. `reduce(lambda x, y: [a+b for a in x for b in y], L)`. Output: `['738', '731', '730', '788', '781', '780']` – citaret Aug 15 '16 at 10:35
I think it is not a duplicate, since `itertools` can not be used. – citaret Aug 15 '16 at 10:42
@citaret thank you very much. But `reduce` also need an extra import. If it is possible to achieve this without import? – Mangosteen Aug 15 '16 at 12:42
Have you tried that? `reduce` is an [Built-in Functions](https://docs.python.org/2/library/functions.html), and you can use it without import. – citaret Aug 15 '16 at 13:27
@citaret: OP is using Python 3 where `reduce` is not a built-in function. – Steven Rumbalski Aug 15 '16 at 15:02
If `L` always has three sublists you can `[int(a)+int(b)+int(c) for a in L[0] for b in L[1] for c in L[2]]` – Steven Rumbalski Aug 15 '16 at 15:03
So, if you use python3, you can implement `reduce` yourself, as in: `xs = L[0]; for ys in L[1:]: xs = [a+b for a in xs for b in ys]` . – citaret Aug 15 '16 at 15:16
@StevenRumbalski sorry, there a plenty of sublists – Mangosteen Aug 15 '16 at 15:20
@Mangosteen: If you can't import `itertools.product` then reimplement it using the example code [from the docs](https://docs.python.org/dev/library/itertools.html#itertools.product) – Steven Rumbalski Aug 15 '16 at 16:28

How to achieve a huge number of for loop in python?

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