tree.py

class Node:
    def __init__(self, name, left, right):
        self.name = name
        self.left = left
        self.right = right

class Tree:
    def __init__(self):
        self.root = Node('1', Node('2', Node('4', None, None), Node('5', None, None)), Node('3', Node('6', None, None), Node('7', None, None)))

    def walk_breadth(self,f):
        q = []
        cur = self.root
        while cur:
            f(cur)
            if cur.left: q.append(cur.left)
            if cur.right: q.append(cur.right)
            if len(q):
                cur = q[0]
                del q[0]
            else: cur = None

if __name__ == "__main__":
    t = Tree()
    def sz(x):
        print x.name
    t.walk_breadth(sz)