Sewed tree

class SewedTreeNode:
    def __init__(self, data = 0):
        self.data = data
        self.left = None
        self.l_thr = False
        self.right = self
        self.r_thr = True

    def set_left(self,left_node, is_thread):
        self.left = left_node
        if True == is_thread:
            self.l_thr = True
        else:
            self.l_thr = False

    def __str__(self):
        l = -1 if None == self.left else self.left.data
        r = -1 if None == self.right else self.right.data
        return "%02d: %02d (%1d), %02d (%1d)" % (self.data, l, self.l_thr, r, self.r_thr)