Django - Amazon S3 · PDF fileDjango ! Jinja2 Aymeric Augustin DjangoCong 2016 Jardin des...

Django 💖

Jinja2 Aymeric Augustin DjangoCong 2016

Jardin des Plantes, Avranches, 9 avril 2016

👋 I’m Aymeric

2

Core Developersince 2011

Chief Technical Officersince 2015

• Time zones• Python 3• Transactions• App loading• Jinja2

First peer-to-peerinsurance broker

in France

We’re hiring!

Amalfi

Why Jinja2?

3

Aren’t Django templates just fine?

4

Jinja2 is fast.10-20x faster than Django templates.

Image from http://www.gentside.com/dragster/wallpaper

5

Django templates are slow.10-20x slower than Jinja2.

Image from https://commons.wikimedia.org/wiki/File:Grand_bi_sur_la_terrasse_Dufferin_vers_1900.jpg

Let’s try it on the fractalideas.com home page!

6

>>> import statistics, timeit

>>> setup = \

... "from django.template.loader import render_to_string"

>>> round(statistics.median(timeit.repeat(

... "render_to_string('home.html', using='django')",

... setup, repeat=10, number=1000)), 2)

1.18 # ms

>>> round(statistics.median(timeit.repeat(

... "render_to_string('home.html', using='jinja2')",

... setup, repeat=10, number=1000)), 2)

0.35 # ms


• More than three times faster!

• Not even a millisecond faster.

• Page loads 0.004% faster with a cold cache.

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• More than three times faster!

• Not even a millisecond faster.

• Page loads 0.02% faster with a warm cache.

8

Template rendering speed (often) doesn’t matter

• Light content? Anything is fast enough

• Heavy static content? Pre-render & cache it

• Heavy dynamic content? Render in the browser

• If you’re thinking about switching template languages, consider both server-side and client-side options (React)

• Until you’ve optimized everything else, templates are unlikely to be a bottleneck

9

Why Jinja2?

10

Aren’t Django templates just fine?

– http://jinja.pocoo.org/docs/

“Jinja2 is a modern and designer-friendly templating language for Python,

modelled after Django’s templates.”

11

Advantages of Jinja2

• More comfortable for developers

• Django expects templates to be written by “designers”

• Easier to customize

• Try writing a Django template tag without the docs

• Meaningfully faster in some use cases

• Template-based widget rendering (#15667)

12

Drawbacks of Jinja2

• Less common than Django templates

• Many authors of pluggable apps don’t know where to start (yet)

• Targets experienced developers

• Docs suggest handling escaping manually for performance

• Scoping behavior for included blocks is declarative

• etc.

13

Features of Jinja2 — from its docs’ homepage

• sandboxed execution

• powerful automatic HTML escaping system for XSS prevention

• template inheritance

• compiles down to the optimal python code just in time

• optional ahead-of-time template compilation

• easy to debug (…)

• configurable syntax14

sounds important (to me)

– paraphrased from http://jinja.pocoo.org/docs/

“Jinja2 is a templating language for Python designed for experienced developers, modelled after Django’s templates.”

15

Third-party solutions

• Coffin (2008 - reborn in 2015)

• Alternative APIs such as render()

• Jingo (2010)

• Template loader (class-based API since Django 1.2)

• Django-Jinja (2012)

• More opinionated and full-featured template loader

16

Templates in Django < 1.8

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Discussed for historical purposes only — these versions are unsupported!

Django < 1.8 - Rendering a template

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# django/template/loaders.py (simplified)

def render_to_string(template_name, dictionary):

template = get_template(template_name, dirs)

context = Context(dictionary)

return template.render(context)


19


def get_template(template_name):

template, origin = find_template(template_name)

return Template(template, origin, template_name)


20


def find_template(name, dirs=None):

global template_source_loaders

if template_source_loaders is None:

... # init from settings.TEMPLATE_LOADERS

for loader in template_source_loaders:

... # try loading with loader(name)

raise TemplateDoesNotExist(name)

global configuration

Django < 1.8 - Actually rendering a template

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# django/shortcuts.py (drastically simplified)

def render(request, template_name, dictionary):

template = get_template(template_name, dirs)

context = RequestContext(request, dictionary)

return HttpResponse(template.render(context))

strong coupling

Context processors are a poor API

• How many context processors depend on request?

• Aside from the request context processor, that is.

• How hard is it to make a context processor lazy?

• In order to avoid overhead in templates that don’t need it.

• Just an API for {{ global_func(request) }}?

• Django templates cannot call functions with arguments.

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Multiple templates engines in Django ≥ 1.8

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If templates weren’t boring, they’d have been fixed earlier.

Plan

1. Write a Django Enhancement Proposal (DEP)

• Lots of reading; some writing

2. Refactor Django templates as a library (optional)

• Actually not optional

3. Implement the DEP

• Sounds easy

27

Concept

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django.template.*

django.template.loader

d.t.backends.django d.t.backends.jinja2

django.template.* jinja2

– DEP 182

“this project avoids encoding the legacy of the Django template language in APIs”

29

Jinja2 for Djangonauts

30

Wake up — this is the “just do this” section.

Install Jinja2

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$ pip install jinja2

Define a Jinja2 environment

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# project/jinja2.py

from jinja2 import Environment

def environment(**options):

options.setdefault('extensions', []).extend([...])

env = Environment(**options)

env.filters.update({ ... })

env.globals.update({ ... })

env.tests.update({ ... })

return env

Install translations (optional)

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# project/jinja2.py

from django.utils import translation

def environment(**options):

# ...

env.install_gettext_translations(translation,

newstyle=True)

# ...

return env

Point the TEMPLATES setting to the environment

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TEMPLATES = [{

'BACKEND': 'django.template.backends'

'.jinja2.Jinja2',

'DIRS': [os.path.join(BASE_DIR, 'templates')],

'OPTIONS': {

'environment': 'project.jinja2.environment',

},

}, {

'BACKEND': 'django.template.backends'

'.django.DjangoTemplates',

'APP_DIRS': True,

}]

Globals

35

# project/jinja2.py

from django.core.urlresolvers import reverse

env.globals.update({

'url': reverse,

})

# templates/header.html

{{ url('account_login') }}

Filters

36

# project/jinja2.py

from urllib.parse import quote

env.filters.update({

'urlquote': quote,

})


?next={{ request.get_full_path() | urlquote }}

Tests

37

# project/jinja2.py

from django.utils.timezone import is_aware

env.tests.update({

'aware': is_aware,

})

# templates/datetime.html

{% if at is aware %}{{ at.tzname() }}{% endif %}

Extensions

38

# project/jinja2.py

options.setdefault('extensions', []).extend([

'jinja2.ext.i18n',

])

# or, alternatively:

env.add_extension('jinja2.ext.i18n')


{{ gettext("Log in") }}

Jinja2 tips

39

You can go back to sleep — the slides will be online.

Calling methods

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# Django templates

{{ qotd }}

# Jinja2

{{ qotd() }}

Inserting the CSRF token in a form

41

# Django templates

{% csrf_token %}

# Jinja2

{{ csrf_input }}

# Both

<input type="hidden"

name="csrfmiddlewaretoken"

value="{{ csrf_token }}" />

Replacing a context processor

42

# project/jinja2.py

from django.contrib.messages import get_messages


'get_messages': get_messages,

})

Replacing a context processor

43


{% for message in get_messages(request) %}

<div>{{ message }}</div>

{% endfor %}

Replacing a context processor - alternative

44

# project/jinja2.py

from django.contrib.messages import get_messages

@jinja2.contextfunction

def _get_messages(context):

return get_messages(context['request'])


'get_messages': _get_messages,

})

Replacing a context processor - alternative

45


{% for message in get_messages() %}

<div>{{ message }}</div>

{% endfor %}

Replacing a template tag

46

# spam/templatetags.py

from django import template

register = template.Library()

@register.simple_tag(takes_context=True)

def eat_spam(context, arg1, arg2):

# ...

return html


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# templates/spam.html

{% load spam %}

{% eat_spam arg1 arg2 %}


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# spam/jinja2.py

@jinja2.contextfunction

def eat_spam(context, arg1, arg2):

# ...

return html

# and register it in env.globals as shown above.


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# templates/spam.html

{{ eat_spam(arg1, arg2) }}

Most extensions only add globals

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# eat/jinja2.py

class EatExtension(Extension):

def __init__(self, env):

env.globals['eat'] = {'spam': eat_spam}

# templates/eat.html

{{ eat.spam() }}

Questions?

Thank you!

Estuaire de la Sée, Avranches, 9 avril 2016

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