Flask-WTForms 如何覆盖单选字段的预验证

当用户在未选择单选选项的情况下提交时，我试图引发错误，但它不起作用。当我像这样渲染字段时：{{ render_field(form.example) }}它打印出(self.gettext('PICK SOMETHING')，但是当我使用下面的格式时没有任何反应：

    {% for subfield in form.religion %}
        {{ render_field(subfield, class_="foo") }}
        {{ render_field(subfield.label) }}
    {% endfor %}

无线电.py

class ReligionField(SelectField):
    widget = ListWidget(prefix_label=False)
    option_widget = RadioInput()

    def pre_validate(self, form):
        for v, _ in self.choices:
            if self.data == v:
                break
        else:
            raise ValueError(self.gettext('PICK SOMETHING'))

class ReligionForm(FlaskForm):
    religions = ['Christian', 'Muslim', 'Hindu', 'Buddhist']
    choices = [(x.lower(), x.title()) for x in sorted(religions)]
    religion = ReligionField('Religion', validators=[DataRequired()], choices=choices, render_kw={"class":"post", "type":"radio"})

@app.route('/',methods=['post','get'])
def hello_world():
    form = ReligionForm()
    if form.validate_on_submit():
        print form.religion.data
    else:
        print form.errors
    return render_template('radio.html', form=form)

我怎样才能覆盖pre_validate如果我在没有选择任何选项的情况下提交，会引发错误吗？

试试这个脚本：

from flask import Flask
from flask import render_template
from flask import request
from flask import flash
from flask import redirect
from flask_wtf import FlaskForm
from wtforms import SelectField
from wtforms.widgets import ListWidget, RadioInput
from wtforms.validators import DataRequired


app = Flask(__name__)

class ReligionField(SelectField):
    widget = ListWidget(prefix_label=False)
    option_widget = RadioInput()

    def pre_validate(self, form):
        for v, _ in self.choices:
            if self.data == v:
                break
        else:
            raise ValueError(self.gettext('PICK SOMETHING'))

class ReligionForm(FlaskForm):
    religions = ['Christian', 'Muslim', 'Hindu', 'Buddhist']
    choices = [(x.lower(), x.title()) for x in sorted(religions)]
    religion = ReligionField('Religion', validators=[DataRequired()], choices=choices, render_kw={"class":"post", "type":"radio"})


@app.route('/',methods=['GET','POST'])
def hello_world():
    form = ReligionForm(request.form)

    if request.method == 'POST':
        if form.validate_on_submit():
        print form.religion.data
        else:
        print form.religion.errors[0]
        flash(form.religion.errors[0])
        return redirect('/')
    return render_template('radio.html', form=form)


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

广播.html

{% with messages = get_flashed_messages() %}
  {% if messages %}
    <ul class=flashes>
    {% for message in messages %}
      <li>{{ message }}</li>
    {% endfor %}
    </ul>
  {% endif %}
{% endwith %}

<form method="post">
{% for subfield in form.religion %}
        <li>{{subfield.label}} {{subfield}} </li>
    {% endfor %}

<button>Submit</button>
</form>