Access to an element of List of lists Python

Question

I have to do a code where I have to change some value in a for loop. I have a list called listElement. I know the exact position of the item that I want to change which is store in a list. For instance [2,2,1] called index (which can also be for instance [3,2] because my listElement is composed of several lists of different sizes).

I would like to do something like this :listElement + index which can create something like listElement[2][2][1] (or listElement[3][2])

listElement = [ "a" , ["b","c"] , [["d"],["e","f"]] ]

tab = [ [2,1,0] , [0] ] # "e" and "a" position

element=""
for i in tab :
    # recuperate the element at the position indicate by i

    element = listElement[i]

Can you show us what you have tried so far, please?

ravi
– ravi

2020-08-20 10:50:22 +00:00
Commented Aug 20, 2020 at 10:50 — ravi
– ravi, Commented Aug 20, 2020 at 10:50

David · Accepted Answer · 2020-08-20 11:02:27Z

2

You could do something like the following:

def recursiveAccess(list, elem):
    if len(elem) == 1:
        return list[elem[0]]
    return recursiveAccess(list[elem[0]], elem[1:])

listElement = [ "a" , ["b","c"] , [["d"],["e","f"]] ]

tab = [ [2,1,0] , [0] ] # "e" and "a" position

for e in tab:
    print(recursiveAccess(listElement, e))
# e
# a

Due to the fact you don't know in advance the access tree to an element of the list a recursive solution is in place. Notice that you should add some checks to validate that the input are always valid.

answered Aug 20, 2020 at 11:02

David

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Booboo · Accepted Answer · 2020-08-20 11:24:49Z

2

Subclass ListElement from list and define method __add__:

class ListElement(list):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)


    def __add__(self, l):
        if not isinstance(l, (list, tuple)):
            raise ValueError('value must be a list or tuple')
        the_list = self
        for inx in l:
            if not isinstance(inx, int):
                raise ValueError('the indices must be ints')
            the_list = the_list.__getitem__(inx)
        return the_list

listElement = ListElement([5, 6, [1, 2], [8, 9, [3, 8, 1]]])
print(listElement + [3, 2])

Prints:

[3, 8, 1]

answered Aug 20, 2020 at 11:24

Booboo

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Comments

Tomerikoo · Accepted Answer · 2020-08-20 11:44:47Z

1

You can just iterate on each index in the indices-list and get the next level each time:

def get_list_element(lst, indices):
    element = lst
    for index in indices:
        element = element[index]
    return element

The following program:

lst = [ "a", ["b", "c"], [["d"], ["e", "f"]] ]
indices_list = [[2,1,0] , [1], []]
for indices in indices_list:
    print(get_list_element(lst, indices))

Will output:

e
['b', 'c']
['a', ['b', 'c'], [['d'], ['e', 'f']]]

edited Aug 20, 2020 at 11:44

answered Aug 20, 2020 at 11:13

Tomerikoo

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