Python – how do I return value from recurrsion

April 13, 2022

I am trying to run this code for search an element in a binary tree. It works well but I cannot return the value but can display it.

Here is my code:

def getNodeAddress(self, data):
        print(self._getNodeAddress(data, self.root))
    
def _getNodeAddress(self, data, root):
        if root:
            if root.data == data:
                print("<<<< ", root.data)
                return root
            self._getNodeAddress(data, root.left)
            self._getNodeAddress(data, root.right)

def _getNodeAddress(self, data, root, res):
        if root:
            if root.data == data:
                print("<<<< ", root.data)
                res = root
            self._getNodeAddress(data, root.left, res)
            self._getNodeAddress(data, root.right, res)
        print(res)
        return res

So in the above method, it traverses the tree to look for the value as the variable key, when it finds one it prints as in the line "print("<<<< ", root.data)", which does display as expected. But now the issue arises when I need to return the value to the parent method which is "getNodeAddress". I cannot print the value in the parent method. It just print "None"
So my question is how do I return the value from a recursion.

I also tried the second approach as in the above code of the same method name, but still exactly the same the issue
Any help would really be appreciated

>Solution :

It looks like only the base case is actually returning anything. You need to add return statements in the non-base cases as well. For example:

def _getNodeAddress(self, data, root):
        if root:
            if root.data == data:
                print("<<<< ", root.data)
                return root
            res = self._getNodeAddress(data, root.left)
            if res is None:
                res = self._getNodeAddress(data, root.right)
            return res