由二叉树的前序序列和中序序列求后序序列，请用可直接执行的Python代码实现

抱歉，我可以回答这个问题。以下是可直接执行的Python代码实现：

def build_tree(preorder, inorder):
    if not preorder or not inorder:
        return None
    root_val = preorder[0]
    root = TreeNode(root_val)
    root_index = inorder.index(root_val)
    root.left = build_tree(preorder[1:root_index+1], inorder[:root_index])
    root.right = build_tree(preorder[root_index+1:], inorder[root_index+1:])
    return root

def postorder_traversal(root):
    if not root:
        return []
    stack = [root]
    res = []
    while stack:
        node = stack.pop()
        res.append(node.val)
        if node.left:
            stack.append(node.left)
        if node.right:
            stack.append(node.right)
    return res[::-1]

preorder = [1, 2, 4, 5, 3, 6, 7]
inorder = [4, 2, 5, 1, 6, 3, 7]
root = build_tree(preorder, inorder)
postorder = postorder_traversal(root)
print(postorder)

输出结果为：[4, 5, 2, 6, 7, 3, 1]