Convert multi-dimensional list to a 1D list in Python

Question

A multidimensional list like l=[[1,2],[3,4]] could be converted to a 1D one by doing sum(l,[]). Can anybody please explain how that happens?

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Answer 1

For any kind of multidiamentional array, this code will do flattening to one dimension :

def flatten(l):
    try:
        return flatten(l[0]) + (flatten(l[1:]) if len(l) > 1 else []) if type(l) is list else [l]
    except IndexError:
        return []