Question

I have a nested list, and I need to reverse every element in the list. But I dont know whether the list is a list of list of list or not.
So example is:

p = [1, [2, 3, [4, [5, 6]]]]
print deep_reverse(p)
#>>> [[[[6, 5], 4], 3, 2], 1]

q =  [1, [2,3], 4, [5,6]]
print deep_reverse(q)
#>>> [ [6,5], 4, [3, 2], 1]

What I have so far is:

def is_list(p):
    return isinstance(p, list)

def deep_reverse(a):
    a.reverse()
    for i in a:
        if is_list(i):
            i.reverse()
            print a

It works well for the second test, the q one, but doest work for the first test.
I am not sure do I need use a recursion to loop the whole thing? How can I modify my code? Thanks.

Answer 1

The reason your code doesn’t work is because if i is a list of lists, you don’t deep_reverse the lists within i.

You only need to change one line of your code to the following:

def is_list(p):
    return isinstance(p, list)

def deep_reverse(a):
    a.reverse()
    for i in a:
        if is_list(i):
            deep_reverse(i)  # <=== This is what changed
            print a