Making list empty after return in function

[micseydel]

There are different solutions, but I prefer to use a closure and a helper function like so

def flatten(to_flatten):
    result = []

    def helper(nested_list):
        for i in nested_list:
            if type(i) != list:
                result.append(i)
            else:
                helper(i)
        return result

    return helper(to_flatten)

Alternatively, you could have a second parameter which defaults to None, and you have have logic which creates the result variable when that parameter is None and then provide it for the recursive calls. I prefer the method I've coded here because it does not change the interface given to clients of the code, who might accidentally provide a second parameter (or who might notice it and wonder).