Question

I am trying to traverse a Binary Tree which is created in the following code. to be precise, the Binary Tree is a class and should include an iterator calling another function namely inorder(). this method should be a recursive generator and yield the value of nodes in every iteration.I tried to create a dictionary to follow the nodes but when I try to call the inorder() method, it doesn’t work. Is there any missing point that I don’t know? I used while and it creates the dictionary of left side of tree (it is a clumsy way).
please help me accomplish this code.

d=[]

# A binary tree class.
class Tree(object):
    def __init__(self, label, left=None, right=None):
        self.label = label
        self.left = left
        self.right = right
        self.d=dict()
    def __repr__(self, level=0, indent="    "):
        s = level * indent + self.label
        if self.left:
            s = s + "\n" + self.left.__repr__(level + 1, indent)
        if self.right:
            s = s + "\n" + self.right.__repr__(level + 1, indent)
        return s

def traverse(self):
    if self.left:
        lastLabel=self.label
        self.left.traverse()
    if self.right:
        lastLabel=self.label
        d.append(lastLabel)
        self.right.traverse()
    else:
        d.append(self.label)
    return d

def __iter__(self):
    return inorder(self)

# Create a Tree from a list.
def tree(sequence):
    n = len(sequence)
    if n == 0:
        return []
    i = n / 2
    return Tree(sequence[i], tree(sequence[:i]), tree(sequence[i+1:]))

# A recursive generator that generates Tree labels in in-order.
def inorder(t):
    for i in range(len(d)):
        yield d[i]    

def test(sequence):
# Create a tree.
    t = tree(sequence)
# Print the nodes of the tree in in-order.
    result = []
    for x in t:
        result.append(x)
    print x
    print

    result_str = ''.join(result)

# Check result
    assert result_str == sequence
    del d[:]
def main():
    # Third test
    test("0123456789")

    print 'Success! All tests passed!'

if __name__ == '__main__':
    main()

I changed my code again
I accomplished the code but I’m sure it is not the best way to traverse a Binary tree.
I defined a method -traverse()- in my class and returned a list of nodes in order now (which at first wasn’t ordered, so I used sort() method.) then I made a loop over this list in my generator, inorder() function, to yield the element of it.
All your comments are very welcome to optimize the code.
please recommend a proper solution based on the specific Tree class in this code.

Answer 1

Perhaps I’m missing something, but I’m not sure why the dictionary is relevant in inorder(). Think about what an in-order traversal looks like in general:

def inorder(t):
    # Process left sub tree
    # Process t
    # Process right sub tree

and so in terms of generators, this would look like:

def inorder(t):
    if t.left:
        for elem in inorder(t.left):
            yield elem
    yield t
    if t.right:
        for elem in inorder(t.right):
            yield elem