def sum_list(L):
    """
    Return L it is's an int, or sum of the numbers in
    possibly nested loop
    @param list | int L: List
    @rtype: int | list
    >>> sum_list(17)
    17
    >>> sum_list([1, [2, 3, [4]], 5])
    15
    """
    if isinstance(L, list):
        return sum([sum_list(x) for x in L])
    else:
        return L


if __name__ == '__main__':
    import doctest
    doctest.testmod()