Recursion: deep sum

A recursive function calls itself on a smaller piece of the problem. Every recursion needs a base case that stops it:

def total(x):
    if isinstance(x, list):
        return sum(total(item) for item in x)  # recurse into each item
    return x                                    # base case: a plain int

isinstance(x, list) asks "is this a list?". This lets one function handle a value that might be a number or a nested list of numbers, at any depth.

Your task

Write deep_sum(x) where x is an int or a (possibly nested) list of ints/lists. Return the sum of every int at any depth.

deep_sum([1, [2, [3, 4]], 5])   # 15
deep_sum([])                    # 0
deep_sum(7)                     # 7

Hint: if isinstance(x, list), return the sum of deep_sum(item) for each item; otherwise x is an int, so just return it.