Print a binary tree, python, in inorder

Question

Me and my friend are doing some school work with programming in Python 3.1 and are VERY stuck. We're programming a binary tree and it's working fine except when we want to print all the nodes in inorder in a way that would create a sentence (all the words in inorder just after one another in a row). We have been looking all over the internet for clues as to how to procede and we've been working with this little thing for like two hours. Any advice/help would be awesome.

Our program/Binary tree:

class Treenode:  
    def __init__(self, it = None, le = None, ri = None):  
        self.item = it  
        self.left = le  
        self.right = ri  

class Bintree:  
    def __init__(self):  
        self.item = None  
        self.left = None  
        self.right = None  

    def put(self, it = None):
        key = Treenode(it)
        if self.item == None:
            self.item = key
            return
        p = self.item
        while True:
            if key.item < p.item:
                if p.left == None:
                    p.left = key
                    return
                else:
                    p = p.left
            elif key.item > p.item:
                if p.right == None:
                    p.right = key
                    return
                else:
                    p = p.right
            else:
                return

    def exists(self, it):
        key = it
        p = self.item
        if p == key:
            return True
        while True:
            if key < p.item:
                if p.left == None:
                    return False
                else:
                    p = p.left
            elif key > p.item:
                if p.right == None:
                    return False
                else:
                    p = p.right
            else:
                return

    def isEmpty(self):
        if self.item == None:
            return True
        else:
            return False

def printtree (Treenode):
    if Treenode.left != None:
        printtree (Treenode.left)
    print (Treenode.item)
    if Treenode.right != None:
        printtree (Treenode.right)

We get a sort of print when we run the program which looks like this: "bintree.Treenode object at 0x02774CB0", which is not what we want.

We use the tree by running this:

import bintree

tree = bintree.Bintree()
print(tree.isEmpty())    # should give True
tree.put("solen")
print(tree.isEmpty())    # should give False
tree.put("gott")
tree.put("sin")
tree.put("hela")
tree.put("ban")
tree.put("upp")
tree.put("himlarunden")
tree.put("manen")
tree.put("seglar")
tree.put("som")
tree.put("en")
tree.put("svan")
tree.put("uti")
tree.put("midnattsstuden")

print(tree.exists("visa"))     # should give False
print(tree.exists("ban"))      # should give True
tree.printtree()               # print sorted

Also, the second last row gives us "None" instead of "True", which is wierd.

Answer 1

print(tree.exists("visa")) returns None, because in the last line of exists() there's return statement without any value (which defaults to None).

Also you shouldn't name a printtree argument Treenode since it's a name of an existing class and that might lead to confusion. It should look more like:

def printtree(tree_node):
    if tree_node.left is not None:
        printtree(tree_node.left)
    print(tree_node.item)
    if tree_node.right is not None:
        printtree(tree_node.right)

Another thing is calling printtree - it's a function, not Bintree method, so I suppose you should call it printtree(tree).