visitBinaryTree_perOrder.py

#coding:utf-8

class treeNode:
    """
    Tree node class
    """
    def __init__(self, value, lnode=None, rnode=None):
        self.value = value
        self.lnode = lnode
        self.rnode = rnode

def DLR(tree):
    """
    per-order visit binary tree
    """
    if tree:
        print tree.value,
        DLR(tree.lnode)
        DLR(tree.rnode)

##execute
if __name__ == "__main__":
    t2 = treeNode(2)
    t3 = treeNode(5)
    t1 = treeNode(3, t2, t3)
    t9 = treeNode(4)
    t6 = treeNode(8,None,t9)
    t7 = treeNode(9)
    t5 = treeNode(7,t6,t7)
    t4 = treeNode(6, t1, t5)
    print 'tree'
    DLR(t4)