FormScribe

FormScribe is a Python 3 library intended to make form validation and processing both easy and correct. It's framework agnostic and test covered. It supports dynamic dependencies and post-validation actions through a declarative API, while using a minimal amount of magic.

How can I install it?

Simply run pip install formscribe. The usage of a virtualenv is highly recommended.

All right, what does it look like?

A simple login form may be implemented in just a few lines. The submit method specifies what should happen once the form is submitted.

HTML

<form role="form" method="post">
    <input name="username" type="text" value="" required>
    <input name="password" type="password" value="" required>
    <button type="submit">Log in</button>
</form>

Python, define the form using FormScribe in the 'forms' module

from formscribe import (Field, Form, ValidationError)
from some_login_implementation import do_login

class LoginForm(Form):
    class Username(Field):
        key = 'username'

        def validate(self, value):
            if not value:
                raise ValidationError('The username is mandatory.')
            return value

    class Password(Field):
        key = 'password'

        def validate(self, value):
            if not value:
                raise ValidationError('The password is mandatory.')
            if len(password) < 6:
                raise ValidationError('The password must be longer than 6 characters.')
            return value

    def submit(username, password):
        return do_login(username, password)

And then in your app, supposing you are using Flask:

from forms import LoginForm
import flask

@app.route('/login/', methods=["GET", "POST"])
def login():
    if flask.request.method == 'POST':
        loginform = LoginForm(flask.request.form)
        for error in loginform.errors:
            flask.flash(error.message)
        if not loginform.errors:
            flask.flash('You were successfully logged in.')
    else:
        return flask.render_template('login.html')

Dynamic dependency support

It is possible to specify a given field should only be validated when another group of fields has also been validated, or when they have a certain value. In the example below, the Clan field will only be validated when the value of race is orc. If it isn't, then that field will be ignored altogether.

from formscribe import (Field, Form, ValidationError)

class CharacterManagement(Form):
    class Race(Field):
        key = 'race'

        def validate(self, value):
            if value not in ('elf', 'orc', 'human'):
                raise ValidationError('Invalid race.')
            return value

    class Clan(Field):
        key = 'clan'
        when_value = {'race': 'orc'}

        def validate(self, value):
            if clan not in ('Raz-bagdur', 'Kaz-faktur', 'Mak-sakur'):
                raise ValidationError('Invalid clan.')
            return value

Changelog

0.3.0

1. Added the enabled Field property, which defines whether a given Field object is enabled or not. Disabled fields aren't taken into account during validation. This property may be a static attribute, a callable, or an actual Python property.
2. A Field's __init__ method may now be used to set attributes, just as you would do with any other Python object. You may then use those attributes normally in the validate() method, since they now belong to the field's instance.

To do

1. Add Python 2.6 and 2.7 support.
2. Add a neat type system, so that code is more reusable and modular.
3. Provide a good way for developers to test their forms without having to emulate global state.
4. Write good documentation using Sphinx.