Why is this function not returning the list of values?-CodePudding

By printing the array "total", I can see that the values are appending correctly. And yet when I print(linked_list_values(a)), it returns None.

a = Node(5)
b = Node(3)
c = Node(9)
total = []
def linked_list_values(head):
  print(total)
  if head == None:
     return None
  total.append(head.num)
  linked_list_values(head.next)
print(linked_list_values(a))

CodePudding user response：

The function returns None because you never have a return statement in it. It does mutate total, but it gets mutated in-place.

Try printing the value of total after the function runs.

>>> linked_list_values(a)
None
>>> total
[5, 3, 9] # Assuming a.next == b and b.next == c

CodePudding user response：

Your function isn't returning anything for the statement at the bottom to print meaning Python is gonna read the return value of your function as None. A simple fix would be to add a return statement after the recursive call.

a = Node(5)
b = Node(3) 
c = Node(9) 
total = [] 
def linked_list_values(head):  
    if head == None:  
        return None 
    total.append(head.num) 
    linked_list_values(head.next)
    return total 
print(linked_list_values(a))