Can i use yield to get the result of all the result in nested function?

Question

I found many code to verify a valid binary tree, but I tried to creat a simple one, however it rise true all the time! Sorry I don't understand the recursion very well.

class TreeNode(object):
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

def is_BST():
        if root:
          return all(is_BST1(root))
def is_BST1(curnode):
        if curnode.right:
          if curnode.right.val>curnode.val:
            is_BST1(curnode.right)
          else:
            yield False
        if curnode.left:
          if curnode.left.val<curnode.val:
            is_BST1(curnode.left)
          else:
            yield False
        else:
          yield True

#tree creation code
    
print(is_BST)

Answer 1

Your main problem is that this line:

        is_BST1(curnode.right)

only returns a generator, but does nothing with it. You should at least iterate on that generator:

    ...
    if curnode.right:
      if curnode.right.val>curnode.val:
        # iterate on the generator built from right node
        for i in is_BST1(curnode.right):
            yield i
      else:
        ...

and of course do the same for the left child...