给定的二叉树结构如下：

#       1
#      / \
#     2   3
#    / \    \
#   4   5   6

完整Python迭代中序遍历的TreeNode类和inorder_iterative函数代码如下：

class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None


def inorder_iterative(root):
    stack = []
    curr = root

    while curr or stack:
        while curr:
            stack.append(curr)
            curr = curr.left
        curr = stack.pop()
        print(curr.val, end=" ")
        curr = curr.right