WTForms is a framework agnostic library handling web forms in python.

Official documentation: WTForms documentation

Basics

Create a form…

class UrlFilterForm(wtforms.Form):
    scheme = wtforms.StringField()
    netloc = wtforms.StringField()
    path = wtforms.StringField()
    query = wtforms.StringField()
    fragment = wtforms.StringField()
```Render it in a jinja2 template...

```python
<form class="form-inline">
    {% for field in form %}
        <div class="form-group">
            {{ field.label }}{% if field.flags.required %}*{% endif %}
            {{ field(class='form-control') }}
        </div>
    {% endfor %}
    <button type="submit" class="btn btn-outline-primary">Submit</button>
</form>

Cookbook

Basic form handler

def handle(self, request):
        form = MyForm(request.form)

        if request.method == 'POST' and form.validate():
            # validation succeeded, handle success here
            return self.redirect('...')

        return self.render_template('...', form=form)

## Basic template (bootstrap enabled)

```jinja2
<form class="form-horizontal" method="post" action="">
    {{ form.some_hidden_field() | safe }}
        
        <!-- ... more hidden fields ... -->
        
        <div class="form-group {% if form.some_field.errors %}has-error{% endif %}">
            {{ form.some_field.label(class="col-sm-2 control-label") }}
            <div class="col-sm-10">
                {{ form.some_field(class='form-control') | safe }}
                {% if form.some_field.errors %}
                    <ul class="errors">{% for error in form.some_field.errors %}<li>{{ error }}</li>{% endfor %}</ul>
                {% endif %}
            </div>
        </div>
        
        <!-- ... more fields ... -->
        
        <div class="form-group">
            <div class="col-sm-offset-2 col-sm-10">
                <button type="submit" class="btn btn-default">Add</button>
            </div>
        </div>
    </form>

Override default once form is instanciated

This cannot be done by setting form.myfield.default after the form is instanciated, because apparently wtforms copy the default value into the field data at this time (see Stack Overflow discussion). You can still override the data.

    form.my_field.data = '...'
```## Dynamically add errors after form validation

```python
    form.my_field.errors.append('Caramba!')