Django

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Django is a web development framework for Python in the same way rails is a framework for Ruby. It is used by a number of major web sites, including Google (i.e., for the Google Application Engine), and can make developing rich web applications much easier.

Django is not an application on its own, however. You will need proficiency in Python programming in order to write an application using Django. If you are not already familiar with Python, a good starting point is Dive Into Python.

Note2 icon.png Note: As of Feb 2012, DH is currently running Django v1.2.3


Setting up Django

Here's how to set up a Django site under your account using Passenger WSGI, which is recommended. Instructions for completing a FastCGI setup are still available at Django FastCGI, but are not recommended — FastCGI is significantly slower, and requires a more complicated setup process. Django can also run under CGI, which is even slower than FastCGI. Don't run Django under CGI.

Step 1 — Set up a shell account

If you don't already have a shell account set up for your domain, you must do so now. See Enabling Shell Access for further instructions.

Step 2 — Configure your domain

You'll need to set up your domain to use Passenger. You can do so by following these steps:

  1. Open the Manage Domains section of the panel, and start editing your domain.
  2. Scroll down to the "Users, Files, and Paths" section. If your web directory does not end with "/public", add that to your web directory.
  3. Once you have done so, scroll down to "Web Options". Turn on the "Passenger" checkbox.
Note2 icon.png Note: If you currently have files under the domain, you must move them into the new "public" directory to make them appear!


Step 3 — Create a database

Any Django site needs a database. If you don't have one prepared already, you can create one through the panel at MySQL Databases. We strongly recommend creating a database just for Django (rather than sharing a database with other applications), as Django does not use a prefix on its table names.

Step 4 — Run the Django setup wizard

SSH into your server, cd into the directory for your application (i.e, the directory which contains your site's public directory, not the public directory itself), and run these commands:

 wget http://wiki.dreamhost.com/django-setup.py
 python django-setup.py

This script will lead you through rest of the the process of setting up your application.

Important icon.png Important: If you receive an error related to line 126 in the Python code, you can fix the script by appending ".py" to the OS call by changing line 126 to look like this:
if os.spawnl(os.P_WAIT, "/usr/bin/django-admin.py", "django-admin.py", "startproject", projname) != 0:


Migrating existing sites from FastCGI to Passenger

Reorganizing your file structure

We recommend reorganizing your directory structure when you migrate to Passenger. If you used the old instructions then you probably have a django_src directory and a django_projects directory. One possible improvement puts everything under a single "django" directory:

 /home/username/django/
   source (your django svn checkout, or skip it and use Dreamhost's site-package of Django)
   projects
   applications (any reusable applications shared between projects)

Assuming you had the old django_src and django_projects directories, the following would move things around, starting from your home directory:

 mkdir django
 mv django_src django/source
 mv django_projects django/projects
 mkdir django/applications

Migrating an existing FastCGI site

  1. Follow the steps above to change your web directory to end with "/public" and enable Passenger on the domain.
  2. Move your static media from its old location to the new public directory.
  3. Adjust the settings.py for your project to point to the new location for the media directory.
  4. Remove the mod_rewrite lines from the .htaccess file in your old web directory, the one that now contains the "public" directory. You'll probably just want to remove the file altogether and create a new one under "public" for the static media, as shown below.
  5. Create a passenger_wsgi.py script in the directory above "public", making sure to add paths to the Django projects and applications directories. If you're using your own Django svn checkout then add the path to that as well. Be sure to replace "username" with your user name and "projectname" with your project name!
 import sys, os
 if sys.version < "2.4": os.execl("/usr/bin/python2.4", "python2.4", *sys.argv)
 sys.path.insert(1, "/home/username/django/source")
 sys.path.insert(1, "/home/username/django/applications")
 sys.path.insert(1, "/home/username/django/projects")
 os.environ['DJANGO_SETTINGS_MODULE'] = "projectname.settings"
 import django.core.handlers.wsgi
 application = django.core.handlers.wsgi.WSGIHandler()

The version check is necessary to force Passenger to use Python 2.4 (for decorator support) on some older servers which default to Python 2.3.

If you were using the locations in the previous Django FastCGI instructions, then you would add only the following to your path instead:

 sys.path.insert(1, "/home/username/django_src")
 sys.path.insert(1, "/home/username/django_projects")

Hints

  • If your application isn't working, double-check usernames, passwords, database names, and hostnames in the settings file.
  • If you make changes to the code, such as working through the official tutorials, and they don't seem to work, make sure to kill any existing python processes and reload the page.
 pkill python
  • If you modified your application and your changes do not seem to be reflected, you may need to notify Passenger about your change by creating or modifying ~/example.com/tmp/restart.txt:
 touch /home/user/example.com/tmp/restart.txt

Passenger looks for this file and reloads the application when this file is modified.

  • If you're using shared hosting and your changes do not seem to be reflected, you can notify Passenger about your change this way: touch passenger_wsgi.py
  • If you installed a custom version of python in your directory and you'd like to use it, add the following to your passenger_wsgi.py file:
 if sys.hexversion < 0x2060000: os.execl("/path/to/your/copy/of/python2.6", "python2.6", *sys.argv)
  • If you're getting meaningless 500 pages even though you have DEBUG enabled in your Django app, you're probably running into a Passenger problem dealing with errors; see Passenger_WSGI#500_Errors_with_Passenger_WSGI_Workaround for help on getting around it.
  • If you're following the Django tutorial or migrating an existing project you may get "Premature end of script headers" in your http error.log. This may be due to the Passenger file not including your project directory in path. One correct solution is to open passenger_wsgi.py and add the following:
 sys.path.append(os.getcwd()+"/<project_name>")

Sending Email

The following is a sample of how to send an email using a dreamhost server.

In your settings.py file:

 EMAIL_HOST = 'mail.yourdomain.com'
 EMAIL_HOST_USER = 'yourmail@yourdomain.com'
 EMAIL_HOST_PASSWORD = 'yourpassword'
 SERVER_EMAIL = DEFAULT_FROM_EMAIL = EMAIL_HOST_USER
 EMAIL_PORT = 587
 EMAIL_USE_TLS = True

Performance Improvements

Shared environment forces users to use some tricks to improve overall performance of web applications. Django provides many ways to do it:

The latter two can be achieved by placing a specially crafted .htaccess in top static file directories (like media/, appmedia/). The one I use is here:

ExpiresActive on
ExpiresDefault "access plus 15 minutes"
ExpiresByType image/gif "access plus 1 hours"
ExpiresByType image/png "access plus 1 hours"
ExpiresByType image/jpeg "access plus 1 hours"
ExpiresByType image/x-icon "access plus 1 hours"
ExpiresByType application/x-javascript "access plus 15 minutes"
ExpiresByType text/css "access plus 1 hours"

SetOutputFilter DEFLATE
BrowserMatch ^Mozilla/4 gzip-only-text/html
BrowserMatch ^Mozilla/4\.0[678] no-gzip
BrowserMatch \bMSIE\s6 no-gzip
BrowserMatch \bMSIE\s7 !no-gzip !gzip-only-text/html
SetEnvIfNoCase Request_URI \
        \.(?:gif|jpe?g|png|pdf|swf|ipk)$ no-gzip dont-vary
Header append Vary User-Agent env=!dont-vary
Warning icon.png Warning: The above file works only for Apache 2.0! If you still use Apache 1.3, please talk to DreamHost support to switch you over to Apache 2.0.


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