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.

Demo

While Django is not a requirement for Ryzom, we currently only have a demo app in Django:

git clone https://yourlabs.io/oss/ryzom.git
sudo -u postgres createdb -O $UTF -E UTF8 ryzom_django_example
cd ryzom
pip install -e .[project]
./manage.py migrate
./manage.py runserver
# open localhost:8000 for a basic form
# open localhost:8000/reactive for databinding with django channels

# 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.

You may also pass component as keyword arguments, in which case they will be have a "slot" attribute and be assigned to self:

yourdiv = Div(main=P('content'))
yourdiv.main == P('content', slot='main')

Special content

Any content that does not define a to_html method will be casted to str and wrapped inside a Text() component.

Any content that is None will be removed from self.content.

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>'

If you don't like to have the attrs after the content of the element, then keep in mind you can also pass content components as keyword arguments.

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 three ways you can write js in Python: the "HTML way", "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.

HTML Way

onclick, onsubmit, onchange and so on may be defined in Python. They will receive the target element as first argument:

class YourComponent(A):
    def onclick(element):
        alert(self.injected_dependency(element))

    def injected_dependency(element):
        return element.attributes.href.value

The above will bundle a YourComponent_onclick function, the YourComponent_dependency function, and recursively.

And YourComponent will render with onclick="YourComponent_onclick(this)".

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:

class YourComponent(Div):
    def nested_injection():
        alert('submit!')

    def on_form_submit():
        self.nested_injection()

    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.html
'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.html.SomeThing'

Register templates for views

Currently, ryzom_django will auto-discover (import) any app's html.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.

Supported API

Low-levels documented in this section are subject to unfriendly change prior to v1 as we are still researching use cases, please use responsibly.

We are trying to secure the following Component methods that you will like to override when refactoring code:

• Component.context(*content, **context): alter the context before rendering to bubble up new context data from inner components to parent components, aiming to solve the same problem we have blocks and extends in jinja templates.
• Component.content_html(*content, **context): render inner HTML
• Component.to_html(*content, **context): renders the outer and inner HTML

Not thread safe

Currently, components are not thread safe because much of its rendering code alters self in a way that will change how it would render again. Some core component code alters self.content during rendering, example in "Special content": "None" case.

Thread safety is an active discussion topic whenever some thread-unsafe code is proposed for merge, but we are not yet certain that this is an issue because of all the better ways Python offers to organize code. For example:

Wrap declarations in lambdas:

class YourView:
    to_button = lambda: YourButton()

Instead of:

class YourView:
    to_button = YourButton()

We are careful with thread safety in new developments, but it seems must convenient to just being able to alter self on the way.

UNIX was not designed to stop its users from doing stupid things, as that would also stop them from doing clever things. — Doug Gwyn