如何设置默认值以选择多个

<select multiple>
  <option value="option1" selected>Option 1</option>
  <option value="option2">Option 2</option>
  <option value="option3" selected>Option 3</option>
  <option value="option4">Option 4</option>
</select>

from flask import Flask, render_template
from flask_wtf import FlaskForm
from wtforms import SelectMultipleField, SubmitField

app = Flask(__name__)
app.config['SECRET_KEY'] = 'your_secret_key'

class MyForm(FlaskForm):
    options = SelectMultipleField('Options', choices=[('option1', 'Option 1'), ('option2', 'Option 2'), ('option3', 'Option 3'), ('option4', 'Option 4')], default=['option1', 'option3'])
    submit = SubmitField('Submit')

@app.route('/', methods=['GET', 'POST'])
def index():
    form = MyForm()
    if form.validate_on_submit():
        selected_options = form.options.data
        # 处理选中的选项
        return f'Selected options: {selected_options}'
    return render_template('index.html', form=form)

if __name__ == '__main__':
    app.run()