在添加另一个节点之前，如何知道一个节点是否已经存在于xml中？

import xml.etree.ElementTree as ET

def is_node_exist(xml_file, node_name):
    tree = ET.parse(xml_file)
    root = tree.getroot()
    
    for node in root.iter():
        if node.tag == node_name:
            return True
    
    return False

# 示例用法
xml_file = 'example.xml'
node_name = 'my_node'

if is_node_exist(xml_file, node_name):
    print(f"The node '{node_name}' exists in the XML.")
else:
    print(f"The node '{node_name}' does not exist in the XML.")