PasteDeploy Application Factory for Django¶

Paste is an umbrella project for widely used WSGI-related packages, as well as the name of a meta-framework part of that project.

One of these projects is PasteDeploy, whose purpose can be implied by its name. Put simply, it offers a very flexible configuration mechanism (based on INI files) to set up your application which can also give you full control over this initialisation by means of Python code. It’s not only used to set up the application in deployment mode, but also in development mode.

The way it works is very simple: You define a callable which takes all the configuration options as arguments and returns a WSGI application object (which in this case would be a Django application). These callables are called “Application Factories”, while Django refers to the WSGI application object as “WSGI handler” or “handler” for short.

If you don’t need to run any initialisation routine, you can have PasteDeploy use the generic Application Factory provided by twod.wsgi. If you do, you can define your own factory. Either way, all these options will be available as settings within Django.

The following is a minimal configuration file which uses the Application Factory provided by twod.wsgi.

[DEFAULT]
debug = False
django_settings_module = your_application.settings

[app:main]
use = egg:twod.wsgi

It does not define any option that can be used by Django or your application, apart from debug. Note this option is lower case: That’s the de-facto spelling for this variable in the WSGI world. twod.wsgi will automatically set Django’s DEBUG to that value.

The DEFAULT section is the only special section in these configuration files. There you can define variables to be used across the different modes in which your application can be run, as well as some meta variables for Paste, twod.wsgi or other 3rd party software. Sections with the app: prefix define the settings for WSGI applications; you should generally use this kind of sections for your settings.

You can have more than one set of settings for your Django application. If, for example, you wanted to be able to use your application in development and deployment mode, you could use a configuration like this:

[DEFAULT]
debug = False
django_settings_module = your_application.settings

[app:main]
use = egg:twod.wsgi

[app:development]
use = main
set debug = True

Because we need to toggle the value of DEBUG from the configuration file, you must remove this variable from your settings module. If you have variables which depend on this value, you can still refer to it like this:

[DEFAULT]
debug = False
django_settings_module = your_application.settings

[app:main]
use = egg:twod.wsgi
TEMPLATE_DEBUG = %(debug)s

[app:development]
use = main
set debug = True

Or, you can override them on a per application basis:

[DEFAULT]
debug = False
django_settings_module = your_application.settings

[app:main]
use = egg:twod.wsgi
TEMPLATE_DEBUG = False

[app:development]
use = main
set debug = True
# TEMPLATE_DEBUG will equal "False" unless we override it:
TEMPLATE_DEBUG = True

You can then use the values the same way you’ve been doing it, with Django’s settings object or the old-way (importing your settings module directly):

from django.conf import settings

print settings.DEBUG

This mechanism can be used to complement your settings module or replace it completely (as long as you don’t use unsupported settings, which must still be set in Python code).

Django settings¶

PasteDeploy passes all the values as strings, so you have to convert them into the right Python type by hand; possibly using the conversion utilities it provides. That’s not necessary with the official settings in Django because twod.wsgi will convert them automatically, and you can also have your own settings converted too.

You can move all your settings to this INI file or only those which should be variable eventually. It’s up to you. The author believes it’s best to move it all to the convenient INI file, except for those settings which are not really settings, but a crucial component of your application (e.g., TEMPLATE_LOADERS, MIDDLEWARE_CLASSES, FILE_UPLOAD_HANDLERS, INSTALLED_APPS)

Strings¶

Because everything is a string unless told otherwise, no extra step is required to use them. You should however keep in mind that quotes should not be used to delimit values – Any quote you put in there will be part of the string.

Examples:

[app:main]
use = egg:twod.wsgi

# Single line option:
MY_SHORT_STRING = foo

MULTI_LINE = This
    is a
    multi-line
    option

# Pound signs are included:
ANOTHER_STRING = Room #12

QUOTED_STRING = "Lorem ipsum"

Booleans¶

Boolean settings in Django like TEMPLATE_DEBUG will be converted automatically, and if you want your boolean settings to be converted automatically too, you can list them all in the DEFAULT section:

[DEFAULT]
# ...
twod.booleans =
    MY_BOOL1
    MY_BOOL2
# ...

[app:main]
use = egg:twod.wsgi
# ...
MY_BOOL1 = True
MY_BOOL2 = False
# ...

Boolean keywords are case-insensitive in PasteDeploy, and you can even use other keywords like yes or no.

Integers¶

Django integer settings like EMAIL_PORT and DATABASE_PORT will get converted automatically if they’re set. Use the twod.integers option to have yours converted too:

[DEFAULT]
# ...
twod.integers =
    MY_INT
# ...

[app:main]
use = egg:twod.wsgi
# ...

# Built-in integer:
DATABASE_PORT = 5432

# Custom integer:
MY_INT = 86400

# ...

Tuples¶

Again, built-in tuple settings in Django are converted automatically. To have your tuples converted too, use the twod.tuples option in the DEFAULT section:

[DEFAULT]
# ...
twod.tuples =
    COLLECTION1
    COLLECTION2
    COLLECTION3
# ...

[app:main]
use = egg:twod.wsgi
# ...

# Single line:
COLLECTION1 = Oxford London Liverpool Leeds Manchester

# Multi line:
COLLECTION2 =
    Oxford
    London
    Liverpool
    Leeds
    Manchester

# Mixed:
COLLECTION3 = Oxford London
    Liverpool Leeds
    Manchester

# ...

Items should be delimited by whitespace.

Note that when you have one of these settings is already defined in your Python settings module, twod.wsgi will append the items found in the INI file to the existing tuple. For example, if you define the following tuple in your settings module:

MIDDLEWARE_CLASSES = (
    'django.middleware.common.CommonMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
)

And have the following configuration:

# ...

[app:main]
use = egg:twod.wsgi

MIDDLEWARE_CLASSES =
    yourpackage.middleware.ExtraMiddleware1
    yourpackage.middleware.ExtraMiddleware2

# ...

The MIDDLEWARE_CLASSES setting will end up having the following value:

tuple(
    'django.middleware.common.CommonMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'yourpackage.middleware.ExtraMiddleware1',
    'yourpackage.middleware.ExtraMiddleware2',
)

Nested tuples¶

Django’s nested tuple settings (e.g., ADMINS) are converted automatically and custom settings can be converted using the twod.nested_tuples:

[DEFAULT]
# ...
twod.nested_tuples =
    YOUR_NESTED_TUPLE
# ...

[app:main]
use = egg:twod.wsgi
# ...
ADMINS =
    Gustavo ; foo@example.com

YOUR_NESTED_TUPLE =
    Europe ; Madrid
    Europe ; Oxford
    Asia ; Tokyo

# ...

Dictionaries¶

Dictionaries can be used almost the same way you use nested tuples:

[DEFAULT]
# ...
twod.dictionaries =
    YOUR_DICTIONARY
# ...

[app:main]
use egg:twod.wsgi
# ...

# Built-in dictionary -- will get converted automatically:
DATABASE_OPTIONS =
    sslmode=require

# Custom dictionary; whitespace surrounding the equals sign is ignored:
YOUR_DICTIONARY =
    France=Paris
    Spain = Madrid
    UK= London
    Venezuela = Caracas

# ...

Settings which can be `None` or a string¶

Some settings need to be either a string or None when resolved to python. Settings which take this form will be converted to None if the value is empty, otherwise they will be left as a string.:

[DEFAULT]
# ...
twod.none_if_empty_settings =
    YOUR_POTENTIALLY_NONE_SETTING
# ...

[app:main]
use egg:twod.wsgi
# ...

# Built-in None value -- will get converted automatically:
FILE_UPLOAD_TEMP_DIR =


# Custom value to be None:
YOUR_POTENTIALLY_NONE_SETTING =

# ...

In this case, the following settings will be available:

>>> from django.conf import settings
>>> print settings.FILE_UPLOAD_TEMP_DIR
None
>>> print settings.YOUR_POTENTIALLY_NONE_SETTING
None

Alternatively these two settings can be defined and will be left as strings:

[DEFAULT]
# ...
twod.none_if_empty_settings =
    YOUR_POTENTIALLY_NONE_SETTING
# ...

[app:main]
use egg:twod.wsgi
# ...

# Built-in None value -- will get converted automatically:
FILE_UPLOAD_TEMP_DIR = /tmp/twod/


# Custom value to be None:
YOUR_POTENTIALLY_NONE_SETTING = Something else

# ...

In this case, the following settings will be available:

>>> from django.conf import settings
>>> print settings.FILE_UPLOAD_TEMP_DIR
/tmp/twod/
>>> print settings.YOUR_POTENTIALLY_NONE_SETTING
Something else

Unsupported settings¶

The following options are not converted automatically, yet:

FILE_UPLOAD_PERMISSIONS.
LANGUAGES.
MESSAGE_TAGS.
SERIALIZATION_MODULES.

New settings introduced in Django 1.2 are not supported yet either.

So, if you need to use them, you would need to define them in your settings module or create your own factory (see below) to convert the values by yourself.

Implicit variables¶

There’s a variable implicitly set by PasteDeploy: here, which is the absolute path to the directory that contains the INI file. You can use it like this:

# ...

[app:main]
use = egg:twod.wsgi
MEDIA_ROOT = %(here)s/media

# ...

The other variable is __file__, which is the absolute path to the INI file. It’s not very useful in the context of these files, but can be useful while using custom factories.

Serving your application¶

Serving your application is a piece of cake now that you use PasteDeploy. It’s simpler than using Django’s mechanisms because there’s no need to import os and set an environment variable.

Deployment¶

The following is a sample WSGI script for mod_wsgi:

from paste.deploy import loadapp

application = loadapp("config:/path/to/your/config.ini")

And the following is a sample script for FastCGI:

from paste.deploy import loadapp
from flup.server.fcgi_fork import WSGIServer

app = loadapp("config:/path/to/your/config.ini")
WSGIServer(app).run()

Sorry for making your deployment boring!

You might want to check the deployment documentation for the other Python frameworks (e.g., Pylons). They’ve been using WSGI heavily since day one, so it’s likely you’ll get ideas on how to meet your special needs, should you have any.

Development server¶

Django’s development server is only able to serve the current Django application using its so-called “handler” with limited WSGI support, so you won’t be able to use manage runserver anymore. But don’t panic! You’ll be able to use a better development server now.

You can use any WSGI compliant server and serve your application with the settings you want to use in development mode. So you could use Apache for development, for example, but we’ve fortunately left the PHP era behind.

There are a few WSGI servers that are very convenient for development of WSGI application and PasteScript is by far the most widely used one. Unlike Django’s, it is multi-threaded and thus suitable for AJAX stuff. Like Django’s, it’s able to reload the application when you change something in your code. It’s also so robust that it’s often the server of choice for people deploying with FastCGI.

Once you have installed PasteScript (e.g., easy_install PasteScript), you need to configure the server in your configuration file by adding the following section anywhere:

[server:main]
use = egg:Paste#http
port = 8080

And then you’ll be able to run the server:

cd /path/to/your/project
paster serve --reload config.ini

paster will load the application defined in app:main. If you want to use a different one, you’d need to set it explicitly, e.g.:

paster serve --reload config.ini#develop

If you don’t want to type that long command all the time, you could just execute that file directly.

Configure logging¶

You can configure logging from the same PasteDeploy configuration file by adding all the sections recognized by Python’s built-in logging mechanisms.

A full development configuration file could look like this:

[server:main]
use = egg:Paste#http
port = 8000

[app:main]
use = config:base-config.ini
set debug = True

# ===== LOGGING

[loggers]
keys = root,yourpackage

[handlers]
keys = global,yourpackage

[formatters]
keys = generic

# Loggers

[logger_root]
level = WARNING
handlers = global

[logger_yourpackage]
qualname = coolproject.module
handlers = yourpackage
propagate = 0

# Handlers

[handler_global]
class = StreamHandler
args = (sys.stderr,)
level = NOTSET
formatter = generic

[handler_yourpackage]
class = handlers.RotatingFileHandler
args = ("%(here)s/logs/coolpackage.log", )
level = NOTSET
formatter = generic

# Formatters

[formatter_generic]
format = %(asctime)s,%(msecs)03d %(levelname)-5.5s [%(name)s] %(message)s
datefmt = %Y-%m-%d %H:%M:%S

Making manage work again¶

You’ll find that your manage command will be broken after moving settings over to a PasteDeploy configuration file. The fix is really simple, just put the following at the top of your manage script:

from paste.deploy import loadapp

loadapp("config:/path/to/your/configuration.ini")

PasteDeploy and Buildout¶

If you’re using Buildout, you may want to use the zc.recipe.egg:scripts recipe to preppend the initialisation code to your scripts. It’d be a powerful tool when your application may be run in different modes.

For example, we’re using it like this:

[buildout]
parts = scripts

# ...

[scripts]
recipe = zc.recipe.egg:scripts
eggs =
    ipython
    OUR_DISTRIBUTION
    sphinx
initialization = from paste.deploy import loadapp; loadapp("${vars:config_uri}")
# "manage" is defined in OUR_DISTRIBUTION
scripts =
    ipython
    manage
    sphinx-build

[vars]
config_uri = config:${buildout:directory}/config.ini

# ...

Tip

If you want to share settings between your PasteDeploy and Buildout configuration files, check DeployRecipes.

Multiple configuration files¶

As we’ve seen so far, PasteDeploy configuration files can be extended in a cascade like fashion. This can also be done across files.

You could have the following base configuration file:

# base-config.ini

[DEFAULT]
debug = False

[app:base]
use = egg:twod.wsgi
EMAIL_PORT = 25

[app:debug]
use = base
set debug = True

And then override it for development:

# develop.ini

[server:main]
use = egg:Paste#http
port = 8080

[app:main]
use = config:base-config.ini#debug
EMAIL_PORT = 1025

This way, you could also run paster as:

paster serve --reload develop.ini

Using custom factories¶

If you need to perform a one-off routine when your application is started up (i.e., before any request), you can write your own PasteDeploy application factory:

from twod.wsgi import wsgify_django

def make_application(global_config, **local_conf):

    # Do something before importing Django and your settings have been applied.

    app = wsgify_django(global_config, **local_conf)

    # Do something right after your application has been set up (e.g., add WSGI middleware).

    return app

global_config is a dictionary that contains all the options in the DEFAULT section, while local_conf will contain all the options in the app:* section.

PasteDeploy offers two options to use application factories in a configuration file:

Setuptools entry point: If you add the following to your setup.py file:

setup("yourdistribution",
  # ...
  entry_points="""
  # -*- Entry points: -*-
  [paste.app_factory]
  main = yourpackage.module:make_application
  """,
)

you’d be able to use the factory as:

# ...
[app:main]
use = egg:yourdistribution
# ...

If you can’t or don’t want to define an entry point, you can use it like this:

# ...
[app:main]
paste.app_factory = yourpackage.module:make_application
# ...

Table Of Contents

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PasteDeploy Application Factory for Django¶

Django settings¶

Strings¶

Booleans¶

Integers¶

Tuples¶

Nested tuples¶

Dictionaries¶

Settings which can be `None` or a string¶

Unsupported settings¶

Implicit variables¶

Serving your application¶

Deployment¶

Development server¶

Configure logging¶

Making manage work again¶

PasteDeploy and Buildout¶

Multiple configuration files¶

Using custom factories¶

PasteDeploy Application Factory for Django¶

Django settings¶

Strings¶

Booleans¶

Integers¶

Tuples¶

Nested tuples¶

Dictionaries¶

Settings which can be None or a string¶

Unsupported settings¶

Implicit variables¶

Serving your application¶

Deployment¶

Development server¶

Configure logging¶

Making manage work again¶

PasteDeploy and Buildout¶

Multiple configuration files¶

Using custom factories¶

Settings which can be `None` or a string¶