Recursively flatten nested lists

Problem

Implement flatten(value). If value is a list, recursively flatten each element; otherwise return a one-element list containing value.

Starter code

def flatten(value):
    pass

Reveal answer or reference solution

def flatten(value):
    if not isinstance(value, list):
        return [value]
    out = []
    for element in value:
        out.extend(flatten(element))
    return out

Public tests

flatten([1,[2,[],[3]],4]) → [1, 2, 3, 4]
flatten(7) → [7]
flatten([]) → []

Local history

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Recursion Practice