如何处理Flask中意外的url参数

from flask import Flask, request

@app.route('/example')
def example():
    param_value = request.args.get('param_name')
    # 处理参数值
    return '参数值为：{}'.format(param_value)

@app.route('/example')
def example():
    param_value = request.args.get('param_name', '默认值')
    # 处理参数值
    return '参数值为：{}'.format(param_value)

@app.route('/example')
def example():
    try:
        param_value = request.args['param_name']
        # 处理参数值
        return '参数值为：{}'.format(param_value)
    except KeyError:
        return '参数不存在'