Ryzom: Replace HTML Templates with Python Components

Why?

Because while frameworks like Django claim that "templates include a restricted language to avoid for the HTML coder to shoot themself in the foot", the GoF on the other hand states that Decorator is the pattern that is most efficient for designing GUIs, which is actually a big part of the success encountered by frameworks such as React.

What?

Ryzom basically offers Python Components, with extra sauce of bleeding edge features such as "compiling Python code to JS", and "data binding" (DOM refreshes itself when data changes in the DB) if you enable websockets.

State

Currently in Beta stage, we are brushing up for a production release in an Open Source project for an NGO defending democracy, with an online voting platform secured with homomorphic encryption, basically a Django project built on top of microsoft/electionguard-python.

It's not ready for general use, but should hopefully be pretty soon... after all, this project has been under R&D sponsored by YourLabs for years now and it's about time!

Demo

git clone https://yourlabs.io/oss/ryzom.git
sudo -u postgres createdb -O $UTF -E UTF8 ryzom_django_example
cd ryzom
pip install -e .
./manage.py migrate
./manage.py runserver

# to run tests:
py.test

Usage

HTML

Content

Components are Python classes in charge of rendering an HTML tag. As such, they may have content (children):

from ryzom.html import *

yourdiv = Div('some', P('content'))
yourdiv.render() == '<div>some <p>content</p></div>'

Most components should instanciate with *content as first argument, and you can pass as many children as needed there. These goes into self.content which you can also change after instanciation.

Attributes

HTML tags also have attributes which we have a Pythonic API for:

Div('hi', cls='x', data_y='z').render() == '<div class="x" data-y="z">hi</div>'

Declarative and inheritance are supported too:

class Something(Div):
    attrs = dict(cls='something', data_something='foo')


class SomethingNew(Something):
    attrs = dict(addcls='new')  # how to add a class without re-defining


yourdiv = SomethingNew('hi')
yourdiv.render() == '<div class="something new" data-something="foo">hi</div>'

Styles

Styles may be declared within attrs or on their own too.

class Foo(Div):
    style = dict(margin_top='1px')

# is the same as:

class Foo(Div):
    style = 'margin-top: 1px'

# is the same as:

class Foo(Div):
    attrs = dict(style='margin-top: 1px')

• Class style attributes will be extracted into a CSS bundle.
• Instance style attributes will be rendered inline.
• Every component that has a style will also render a class attribute.

JavaScript

This repository provides a py2js fork that you may use to write JavaScript in Python. There are two ways you can write js in Python: the "jQuery way" and the WebComponent way.

You must however understand that our purpose is to write JS in Python, rather than supporting Python in JS like the Transcrypt project. In our case, we will restrict ourselves to a subset of both the JS and Python language, so things like Python __mro__ or even multiple inheritance won't be supported at all.

However, you can still write JS in Python and generate a JS bundle.

WebComponent: HTMLElement

The following defines a custom HTMLElement with a JS HTMLElement class, it will generate a basic web component.

class DeleteButton(Component):
    tag = 'delete-button'

    class HTMLElement:
        def connectedCallback(self):
            this.addEventListener('click', this.delete.bind(this))

        async def delete(self, event):
            csrf = document.querySelector('[name="csrfmiddlewaretoken"]')
            await fetch(this.attributes['delete-url'].value, {
                method: 'delete',
                headers: {'X-CSRFTOKEN': csrf.value},
                redirect: 'manual',
            }).then(lambda response: print(response))

This will generate the following JS, which will let the browser responsible for the components lifecycle, check window.customElement.define documentation for details.

class DeleteButton extends HTMLElement {
    connectedCallback() {
        this.addEventListener('click',this.delete.bind(this));
    }
    async delete() {
        var csrf = document.querySelector('[name="csrfmiddlewaretoken"]');
        await fetch(this.attributes['delete-url'].value,{
            method: 'delete',
            headers: {'X-CSRFTOKEN': csrf.value},
            redirect: 'manual'
        }).then(
            (response) => {return console.log(response)}
        );
    }
}

window.customElements.define("delete-button", DeleteButton);

And that's pretty rock'n'roll if you ask me.

BUT there is a catch: currently, you must set the first argument to self like in Python, so that the transpiler knows that this function is a class method and that it shouldn't render with the function prefix that doesn't work in ES6 classes.

The jQuery way

You can do it "the jQuery way" by defining a py2js method in your component with the py2js.Mixin:

class YourComponent(py2js.Mixin, Div):
    def on_form_submit():
        alert('submit!')

    def py2js(self):
        getElementByUuid(self._id).addEventListener('submit', self.on_form_submit)

This will make your component also render the addEventListener statement in a script tag, and the bundle will package the on_form_submit function.

Bundles

The component will depend on their CSS and JS bundles. Without Django, you can do it manually as such:

from ryzom import bundle

your_components_modules = [
    'ryzom_mdc.html',
    'your.html',
]

css_bundle = bundle.css(*your_components_modules)
js_bundle = bundle.js(*your_components_modules)

Django

INSTALLED_APPS

Add to settings.INSTALLED_APPS:

'ryzom',            # add py-builtins.js static file
'ryzom_django',     # enable autodiscover of app_name.components
'ryzom_django_mdc', # enable MDC form rendering

TEMPLATES

While ryzom offers to register components to template names, ryzom_django offers the template backend to make any use of that with Django, add the template backend as such in settings.py:

TEMPLATES = [
    {
        'BACKEND': 'ryzom_django.template_backend.Ryzom',
    },
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [],
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',
            ],
        },
    },
]

This template backend will allow two usages:

• overriding html template names with components,
• using components import path in dotted-style for template_name, ie. template_name = 'yourapp.components.SomeThing'

Register templates for views

Currently, ryzom_django will auto-discover (import) any app's components.py file. As such, this is where you can define all your view templates replacements with ryzom.html.template. For example, to set the default template for a django.views.generic.ListView with model YourModel:

from ryzom_mdc import *

class BaseTemplate(Html):
    title = 'Your site title'


@template('yourapp/yourmodel_list.html', BaseTemplate)
class YourModelList(Ul)
    def __init__(self, **context):
        super().__init(*[Li(f'{obj}') for obj in context['object_list'])])

Import the html module from ryzom_mdc or from ryzom, depending on the flavor you want. You can nest components on the fly as you register a template, which replaces {% extends %}.

You may chain as many parents as you would like, for example you could have a "card" layout that sets a small content width:

class CardLayout(Div):
    style='max-width: 20em; margin: auto'

@html.template('yourapp/yourmodel_form.html', BaseTemplate, CardLayout)
class YourModelForm(Form):
    def __init__(self, **context):
        super().__init__(
            CSRFInput(context['view'].request),
            context['form'],
            method="post",
        )

Bundles

ryzom_django app provides 3 commands:

• ryzom_css: output the CSS bundle
• ryzom_js: output the JS bundle
• ryzom_bundle: write bundle.js and bundle.css in ryzom_bundle/static

As well as 2 views, JSBundleView and CSSBundleView that you can use in development, include them in your urls.py as such:

from django.conf import settings

if settings.DEBUG:
    urlpatterns.append(
        path('bundles/', include('ryzom_django.bundle')),
    )

For production, you may write the bundles before running collectstatic as such:

./manage.py ryzom_bundle
./manage.py collectstatic

Then, make sure you use the Html component from ryzom_django or any ryzom_django_* app, which will include them automatically.

Forms

API

ryzom_django.forms patches django.forms.BaseForm with 2 new methods:

• BaseForm.to_html(): render the HTML, makes the BaseForm objects "quack" like a component, also useable in non-ryzom templates to get the rendering with {{ form.to_html }}

• BaseForm.to_component(): called by to_html(), this is where the default layout is generated, which you can override to customize the form object rendering. It will return a CList (tagless component list) of the to_component() result of every boundfield.

ryzom_django.forms patches django.forms.BoundField with 2 new methods:

• BoundField.to_component(): this will return the Component template registered for the field widget template name if any, in which case it will use the from_boundfield(boundfield) of that template.

• BoundField.to_html(): render the HTML, makes the BoundField objects "quack" like components.

As such, you can configure how a form object renders by overriding the to_component() method, and use BoundField objects like components too:

def to_component(self):
    return Div(
        H3('Example form!'),
        self['some_field'],  # BoundField quacks like a Component!
        Div(
            Input(type='submit'),
        )
    )

Demo

An example Django project is available in src/ryzom_django_example/, example code is in the urls.py file.