python - Using recursion in a class

Question

I'm practicing for an exam and trying to figure this out. I'm just not exactly what to do with the add method. This is what I have so far:

class recursion:
    def __init__(self, lst=[]):
        self.lst = lst

    def add(self, x, y):
        return x + y

    def recurs(self):
        if len(self.lst) == 1:
            return lst[0]
        else:
            return self.lst[0].add(self.recurs(lst[1:])

Answer 1

Assuming you're trying to recursively get the sum of the list:

Essentially, recursive_sum_helper keeps calling itself with smaller lists:

sum(1, 2, 3, 4) = 1+sum(2,3,4) = 1+( 2 + sum(3,4) ) = ...

class recursive_summer:
    def __init__(self, lst=[]):
        self.lst = lst
    def recursive_sum(self):
        return self.recursive_sum_helper(self.lst)
    def recursive_sum_helper(self, a_lst):
        if len(a_lst) == 1:
            return a_lst[0]
        else:
            first_element = a_lst[0]
            list_without_first_element = a_lst[1:]
            return first_element + self.recursive_sum_helper( list_without_first_element )

r = recursive_summer([1,2,3,4])
r.recursive_sum()

The output is 10.

Hope this helps with whatever problem you're trying to solve.