Question

I expet that this code should output:

8
8

but it does not.

class tree:
    def __init__(self, size=2):
        if size == 0:
            return None
        if size > 1:
            half = size//2
            self.left = tree(size-half)
            self.right = tree(half)
        else:
            self.left = self.right = None
        self.free = size
        self.size = size

    def resize(self,n):
        while self.size < n:
            t = tree(0)
            t.left = self
            t.right = tree(self.size)
            t.free = t.left.size + t.right.size
            t.size = self.size * 2
            self = t
        print("size in resize", self.size)

t = tree()
t.resize(5)
print("size of t", t.size)

output:

size in resize 8
size of t 2

I know I could do return self in resize and t = tree.resize(5) in main, but what if I want to return something else?

Answer 1

Karl’s answer is entirely right about everything, but there is certainly a way to make resize act as you’re expecting.

Three steps:

1. Make a copy of the tree
2. Re-initialize the tree so it’s the next size larger

3. Set the enlarged tree’s left to the copy of the original tree

   def resize(self,n):
           while self.size < n:
               new = self.copy()
               self.__init__(int(round(self.size, 2)) * 2)
               self.left = new
   
           print("size in resize",self.size)
   
   def copy(self):
           new = tree(1)
           new.left = self.left
           new.right = self.right
           new.size = self.size
           new.free = self.free
           return new
   

Basically, you were trying to do it backwards — replace self and reuse self for self.left, instead of replacing self.left and reusing self.