烧瓶动态复选框

这非常简单:我有一个ID列表,我想将它们作为一系列复选框显示给用户。用户应该选择他想要的,然后检查选择了哪些,并执行一个函数。这是我的密码:

from flask import Flask, render_template, flash, request, redirect
from wtforms import Form, TextField, TextAreaField, validators, StringField, SubmitField,widgets, SelectMultipleField
from flask_wtf import FlaskForm

app = Flask(__name__)
app.config.from_object(__name__)
@app.route("/example", methods=["GET", "POST"])
    def example():
      form = FlaskForm()
      ids= ['a','b','c']
      if request.method == 'POST':
          selected_ids = request.form.getlist("ids")
          if form.validate():
              flash('nice')
          else:
              flash('something went wrong')

      return render_template('example.html', form=form, ids= ids)

还有我的模板。html:

<div class="container"> 
    <div class="content-section">
        <form method="POST" action="">
            <fieldset class="form-group">
                <legend class="border-bottom mb-4">IDs to select</legend>
                {%for i in ids%}
                <li>
                        <input type = "checkbox" id = "id_{{i}}" name = "ids" value = "1">
                        <label for="id1">{{i}}</label>
                 </li>
                {% endfor %}

            </fieldset>
        <button type="submit" class="btn btn-success">GO</button>
        </form>
    </div>

但是,当我提交时,这会产生一个500错误。我哪里做错了?非常感谢您的任何建议!