how to get the declaration of a list done during the unnesting recursively?
<p>I have been getting my head around to do the recursion <strong>without using any global variable</strong>. If am passing the lists the lists of lists ... and resultantly, i should have all the elements from the input in a single list. The problem is every time i call the function the list is declared from the start. </p>

<pre><code>    def unnest (alist):  
        List_ = list()

        for elements in alist: 
            if type(elements) == list: 
                unnest(elements)
            else: 
                List_.append(elements)
        return List_
    if __name__=='__main__':
        unnest([1,2,[3,4,5,[6,7,[8,9,[10,11,[12,[13,[14]]]]]]]])
</code></pre>

<p>You have to use the returned <code>List_</code>, in subsequent calls, and extend the current list:</p>

<pre><code>def recursion (alist):
    List_ = list()

    for elements in alist:
        if type(elements) == list:
            List_.extend(recursion(elements))  # extend list with recursive call
        else:
            List_.append(elements)  # just add "leaf" element
    return List_

if __name__=='__main__':
    z=recursion([1,2,[3,4,5,[6,7,[8,9,[10,11,[12,[13,[14]]]]]]]])
    print(z)
</code></pre>

<p>output:</p>

<pre><code>[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
</code></pre>

python python-3.x recursion