RadioFields using WTForms in Flask

forms.py

from flask_wtf import FlaskForm
from wtforms import TextAreaField, SubmitField, RadioField
from wtforms.validators import DataRequired


class HtmlForm(FlaskForm):
    html = TextAreaField(
        "Paste exported html", validators=[DataRequired()]
    )
    hosts = [("s1", "S1"), ("b2", "B2")]
    host_option = RadioField("Label", choices=hosts, default="b2")
    submit = SubmitField("Process")

index.html

{% extends "base.html" %}

{% block content %}
    <h1>Process HTML</h1>
    <form action="" method="post" novalidate>
        {{ form.hidden_tag() }}
        <p>
            {{ form.html.label }}<br>
            {{ form.html(rows='30',cols='100') }}
            {% for error in form.html.errors %}
                <p style="color: red;">[{{ error }}]</p>
            {% endfor %}
        </p>
        <p>Select host destination</p>
        {% for subfield in form.host_option %}
            <tr>
                <td>{{ subfield }}</td>
                <td>{{ subfield.label }}</td>
            </tr>
        {% endfor %}
        <p>{{ form.submit() }}</p>
    </form>
{% endblock %}

main.py

from flask import Flask, flash, render_template, redirect, url_for, request

from config import Config
from forms import HtmlForm


app = Flask(__name__)
app.config.from_object(Config)

@app.route("/", methods=["GET", "POST"])
def index():
    form = HtmlForm()
    if form.validate_on_submit():
#         DO SOMETHING
        pass
        return redirect(url_for("processed", processed_html=processed_html))
    return render_template("index.html", title="Export", form=form)