Python Flask WTForms custom validator does not work

Question

I am trying to create a custom URL validator for a form input field but validator does not seem to work. I applied a DataRequired() to the StringField which works fine but the custom validator does not. Here is code:

def validate_domain(form, field):
    url_regex = r'''((http|https)\:\/\/)?[a-zA-Z0-9\.\/\?\:@\-_=#]+\.
                ([a-zA-Z]){2,6}([a-zA-Z0-9\.\&\/\?\:@\-_=#])*'''
    regex = re.compile(url_regex)
    url = regex.match(field.data).group()
    if url:
        field.data = 'http://' + urlparse(url).netloc
    else:
        raise ValidationError('Please enter a valid URL.')


class SubmitDomainForm(Form):
    domain = StringField('Domain', validators=[DataRequired(),
                         validate_domain])
    submit = SubmitField('Crawl')

HTML for the same:

{% extends "layout.html" %}
{% block content %}
<div class="content-section">
    <form method="POST" action="">
        {{ form.hidden_tag() }}
        <fieldset class="form-group">
            <legend class="border-bottom mb-4">{{ legend }}</legend>
            <div class="form-group">
                {{ form.domain.label(class="form-control-label") }}
                {% if form.domain.errors %}
                    {{ form.domain(class="form-control form-control-lg is-invalid") }}
                    <div class="invalid-feedback">
                        {% for error in form.domain.errors %}
                            <span>{{ error }}</span>
                        {% endfor %}
                    </div>
                {% else %}
                    {{ form.domain(class="form-control form-control-lg") }}
                {% endif %}
            </div>
        </fieldset>
        <div class="form-group">
            {{ form.submit(class="btn btn-outline-info") }}
        </div>
    </form>
{% endblock content %}

Even when I submit a non URL input the form just submits. I am unable to get what seem to going wrong here.

Answer 1

After testing my comment it seems that multi-lining your regex is likely causing you an issue

import re
from urllib.parse import urlparse

data = 'https://google.com/#resource'

url_regex = r'''((http|https)\:\/\/)?[a-zA-Z0-9\.\/\?\:@\-_=#]+\.([a-zA-Z]){2,6}([a-zA-Z0-9\.\&\/\?\:@\-_=#])*'''
regex = re.compile(url_regex)
url = regex.match(data).group()
print('http://' + urlparse(url).netloc)

the above code works for me.