Unpacking n-level nested lists

Question

Suppose, I have a list,

[(1,2), (3, 4)].

I will print 1 + 2 and 3 + 4 if all elements of the list are tuples. But if any one of the elements is also a list, then I add 1 to every element of the inner list and every element of that inner list is appended to the parent list. eg.

list = [(1,2), [(3, 4), (5, 6)]],

becomes

[(1, 2), (3, 4, 1), (5, 6, 1)].

Again, if the inner list has a list as an element, we repeat the same thing. eg.

[(1,2), [(3, 4), (5, 6), [(7, 8)]]]

first becomes

[(1,2), [(3, 4), (5, 6), (7, 8, 1)]]

then finally becomes,

[(1,2), (3, 4, 1), (5, 6, 1), (7, 8, 1, 1)].

How do I do this procedure to such a list, whose nesting level(as in list in a list in a list....) is not known ?

The code I used to generate this list is as follows:

def possible_sums(a):
    if a == 2:
        return [(1, 1)]
    list_l = list(((a - 1, 1), ))
    list_l.append(possible_sums(a-1))
    return list_l


print(possible_sums(8))

I think that the additional requirements (detecting tuples vs. lists, modifying the tuples) sufficiently differ this from that duplicate. — Patrick Haugh, Aug 29 '18 at 14:37

score 3 · Accepted Answer · answered Aug 29 '18 at 14:47

This solution uses nested generators. We loop through the items of our list, checking their types. Whenever we see a list, we recursively call flatten on that list, and add 1 to the end of each output. If item is a tuple, we just yield it. Then outside flatten, we iterate though the generator to build a list.

def flattener(lst):
    for item in lst:
        if isinstance(item, list):
            gen = flattener(item)
            for item in gen:
                yield item + (1,)
        elif isinstance(item, tuple):
            yield item


print(list(flattener([(1,2), [(3, 4), (5, 6), [(7, 8)]], [(5, 6, 7), [(1, 2)]]])))
# [(1, 2), (3, 4, 1), (5, 6, 1), (7, 8, 1, 1), (5, 6, 7, 1), (1, 2, 1, 1)]

https://stackoverflow.com/questions/11984386/expand-and-flatten-a-ragged-nested-list — DYZ, Aug 29 '18 at 14:51

Tanmay jain · Answer 2 · 2018-08-30T03:47:00.813

nested_lst = [(1,2), [(3, 4), (5, 6), [(7, 8)]] ,(2,3),[(6,7)]] 
output = []

def de_nestify(lst,lvl):

    if len(lst) != 0:
        for item in lst:
            if isinstance(item, list):
                lvl += 1
                de_nestify(item,lvl)
                lvl = 0 #reset nesting lvl

            else:
                item += (1,)*lvl
                output.append(item)


de_nestify(nested_lst,0)

print(output) 
#[(1, 2), (3, 4, 1), (5, 6, 1), (7, 8, 1, 1), (2, 3), (6, 7, 1)]

Unpacking n-level nested lists

2 Answers2