Pluggable Django Application Patterns PyCon 2011

Pluggable Patterns
For Reusable Django Applications

Friday, March 11, 2011

An app MyBlog App
should not be • Categories
• Custom Tagging
a monolithic • Custom Comments
pile of code • Comment
Moderation
• Assumption of text
markup type
• Single blogs
For example, most blog • Multiple Sites
“apps” available provide
too much functionality ACME MONOLITHS

An application should
be “pluggable”


A “pluggable” app is
Focused
Write programs that do one thing and do it well.
— Doug McIlroy (inventor of UNIX pipes)


Self-Contained
Batteries are included
Dependencies are declared


Easily Adaptable
Corey’s Law: The less adaptable you make your code, the
sooner you will be tasked to adapt it.


Easily Installed
pip install coolapp
You did declare your dependencies, right?


How do we make a
“pluggable” application?


Stop thinking like this

http://upload.wikimedia.org/wikipedia/commons/archive/a/aa/20090315161532!Ferrari_Enzo_Ferrari.JPG

and think like this


Applications can have
very different purposes

http://www.flickr.com/photos/tiemposdelruido/4051083769/

Application Types
• Data. Manages specific data and access to it
• Utility. Provide aapplication a specific
problem for any
way of handling

• Decorator.functionality of many applications
aggregates
Adds functionality to one or


Situation 1

You want to configure your app
without modifying its code
(e.g. API keys)


Configurable Options
Django Supertagging http://github.com/josesoa

Internal Name Setting Name Default Value


Configurable Options
Django Debug Toolbar http://github.com/robhudson


Data Apps

http://www.flickr.com/photos/29276244@N03/3200630853/

Situation 2

Lots of variations
Each implementation is different
(e.g. blogs)


Abstract Models
GLAMKit http://www.glamkit.org/

EntryBase

FeaturableEntryMixin

StatusableEntryMixin

TaggableEntryMixin

HTMLFormattableEntryMixin


Situation 3

A few, well-known of variations
(e.g. Use django.contrib.sites?)


Optional Field Settings


Situation 4

Optionally use another
application
(e.g. Use django-tagging?)


Optional Integration


Situation 5

You want to reference
different models
(e.g. Customizable author field)


Runtime Configurable
Foreign Keys
Viewpoint http://github.com/washingtontimes


Utility Apps

http://www.flickr.com/photos/s8/3638531205/

Required for
template tags or
management commands

Decorator Apps

http://www.flickr.com/photos/yum9me/2109549869/

New Method New Field

Custom Manager New Admin


Situation 6

You want to add a
field to a model


Lazy Field Insertion
Django Categories http://github.com/washingtontimes


Situation 7

You want to add a
custom manager to a model


Lazy Manager Insertion
Django MPTT http://github.com/django-mptt


Adding a manager
Django MPTT http://github.com/django-mptt
from django.db.models import get_model
import django.conf import settings
from coolapp.managers import CustomManager

MODELS = getattr(settings, 'COOLAPP_MODELS', {})

for model_name, mgr_name in MODELS.items():
if not isinstance(model_name, basestring):
continue

model = get_model(*model_name.split('.'))

if not getattr(model, mgr_name, False):
manager = CustomManager()
manager.contribute_to_class(model, mgr_name)


Situation 8

You want to customize
a model’s ModelAdmin
(e.g. Change the widget of a field)


Lazy Registration of a
Custom ModelAdmin
Django TinyMCE http://github.com/justquick

project’s settings.py

Custom ModelAdmin

Django-TinyMCE’s models.py

Custom ModelAdmin

Django-TinyMCE’s admin.py

Custom ModelAdmin

bottom of Django-TinyMCE’s admin.py

Touch Points


Touch Points of an App

The parts of an application that
usually need tweaking
• URLs
• Templates
• View responses


Situation 9

You want the URLs of your app to
live under any prefix
(e.g. /blogs/ vs. /weblogs/)


Name your URLs


Name your URLs

url Function name


Reference your
URLs by name


Situation 10

You want your templates
to be easily overridable


“Namespace” Templates
All templates in
coolapp a template
“name space”
templates

coolapp

base.html


“Namespace” Templates
coolapp

templates

coolapp

Referenced as base.html
“coolapp/base.html”


Extend one template
site_base.html base.html

summary.html index.html detail.html

Extend one template
site_base.html base.html

base.html

summary.html index.html detail.html

Extend one template

coolapp/base.html

Import your blocks
Allows you to override any of the templates

extra_head.html

coolapp/detail.html

Situation 11

You want flexibility storing
uploaded files


Define a Storage Option


Situation 12
You want to alter the
data your views use
(e.g. Extra context, different
template)


100% more class-
based views!

django-cbv for
backwards
compatibility!

My Info

• coreyoordt@gmail.com
• @coordt
• github.com/coordt
• github.com/washingtontimes
• opensource.washingtontimes.com


Pluggable Django Application Patterns PyCon 2011

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