WtForms Demo

main.j2

<form method="POST" action="/">
{% if form.errors %}
    <div>
    <ul class="errors">
        {% for field_name, field_errors in form.errors|dictsort if field_errors %}
            {% for error in field_errors %}
                <li>{{ form[field_name].label }}: {{ error }}</li>
            {% endfor %}
        {% endfor %}
    </ul>
    </div>
{% endif %}
    <div>
        <label>{{ form.username.label }}:</label>
        {{ form.username() }}
    </div>
    <div>
        <label>{{ form.email.label }}:</label>
        {{ form.email() }}
    </div>
    <div>
        <label>{{ form.birthday.label }}:</label>
        {{ form.birthday() }}
    </div>
    <button type=submit>SUBMIT</button>
</form>

main.py

#!/usr/bin/env python3

from flask import Flask, request, render_template, url_for, redirect
from wtforms import Form, validators, DateField, StringField

app = Flask(__name__)


class TestForm(Form):
    username: str = StringField("Username", [validators.Length(min=4, max=25)])
    email: str = StringField("Email", [validators.email()])
    birthday: str = DateField("Birthday", format="%m/%d/%Y")


@app.route("/done")
def done():
    return "Molodets"


@app.route("/", methods=["GET", "POST"])
def home() -> str:
    if request.method != "POST":
        return render_template("main.j2", form=TestForm())

    form = TestForm(request.form)
    if request.method == "POST" and form.validate():
        return redirect(url_for("done"))
    return render_template("main.j2", form=form)


if __name__ == "__main__":
    app.run(host="0.0.0.0", port=5000, debug=True)