Question

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Flatten (an irregular) list of lists in Python

I have a list in python like

l=[1,2,[3,4,5],[[4,2,4],[4,7,8]]]

I want using a set to get all unique values, but this fails

set(l)

TypeError: unhashable type: 'list'

So anybody help please? Want to use set with list of list of list etc etc THX

Answer 1

You’ll need to ‘unwind’, or flatten the nested structure before you can put this in a set. You can use a generator for that to keep this efficient for large lists:

def flatten(lst):
    for element in lst:
        if isinstance(element, list):
            for subelement in flatten(element):
                yield subelement
        else:
            yield element

then use that generator on your list l to create a set:

set(flatten(l))