How to change certain elements in multidimensional list via function - Python 3-x

Question

i've been spending some time on this, but i'm still learning and haven't managed to do it. Well partialy i did, but i don't want the entering variable to be changed.

def changeit(element, value1, value2):
    if type(element) == list:
        for index, element2 in enumerate(element):
            if element2 == value1:
                element[index] = value2
            if type(element2) == list:
                changeit(element2, value1, value2)
            if value1 not in element:
                return element

def changelist(inputlist, value1, value2):
    for index, element in enumerate(inputlist):
        if type(element) == list:
            changeit(element, value1, value2)
        if element == value1:
            inputlist[index] = value2
    return inputlist

So the function should replace all value1 for value2. The desired output would be:

>>> k = [[[7]], 8]
>>> print(changelist(k, 7, 'a'))
[[['a']], 8]
>>> k
[[[7]], 8]

but so far i'm getting:

>>> k = [[[7]], 8]
>>> print(changelist((k,7,"x"))
[[['x']], 8]
>>> k
[[['x']], 8]

And i just can't find a way how to not change the entering list. Thanks!

If you don't want to change the list, you need to build a new list and return that. — Patrick Haugh, Jan 05 '18 at 17:34
So i just tried by simply inserting new_list = inputlist at the beginning and changing everything mentioning inputlist to new_list. But i got the same result. — A Student, Jan 05 '18 at 17:38
You just referenced the existing list instead of copying it. new_list = list(inputlist) would create a new unique ID'd list. — Aaron Lael, Jan 05 '18 at 17:41
Oh thank you, but unfortunately i'm still getting the same result. — A Student, Jan 05 '18 at 17:44
[What exactly is the difference between shallow copy, deepcopy and normal assignment operation?](https://stackoverflow.com/q/17246693/6779307) — Patrick Haugh, Jan 05 '18 at 17:46
Thank you for your interest! Will continue to study for sure. :) — A Student, Jan 05 '18 at 17:53

score 0 · Accepted Answer · answered Jan 05 '18 at 17:44

0

def replace(l, old, new):
    return [new if x == old else replace(x, old, new) if isinstance(x, list) else x for x in l]

Here's a recursive solution using list comprehensions. This is equivalent to

def replace(l, old, new):
    ret = []
    for x in l:
        if x == old:
            ret.append(new)
        elif isinstance(x, list):
            ret.append(replace(l, old, new))
        else:
            ret.append(x)
    return ret

answered Jan 05 '18 at 17:44

Patrick Haugh

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Thank you very much! Have to learn more about list comprehensions that's for sure. :) – A Student Jan 05 '18 at 17:47

How to change certain elements in multidimensional list via function - Python 3-x

1 Answers1