def sum(lst, var=0): """Returns the sum of the list usng recursion.""" if len(lst) == 0: return var #base case return sum(lst[2:], var + lst[0])

The function takes a list and a variable (var) which is the sum of the list. The function then calls itself on the list with the first two values added together and added to the var. The function then calls itself with the next two values added together and added to the var again until there are no values left in the list and the function returns the value of var.