recursive function for extract elements from deep nested lists/tuples

Question

I want to write a function that extracts elements from deep nested tuples and lists, say I have something like this

l = (\'THIS\', [(\'THAT\', [\'a\', \'b\']),          


        

Answer 1

Assuming that the first element of each tuple can be disregarded, and we should recurse with list that is the second element, we can do this:

def extract(node):
    if isinstance(node, tuple):
        return extract(node[1])
    if isinstance(node, list):
        return [item for sublist in [extract(elem) for elem in node] for item in sublist]
    return node

The list comprehension is a little dense, here's the same with loops:

def extract(node):
    if isinstance(node, tuple):
        return extract(node[1])
    if isinstance(node, list):
        result = []
        for item in node:
            for sublist in extract(item):
                for elem in sublist:
                    result.append(elem)
        return result
    return node