Thursday, December 20, 2012

How to use Shovel with Django

Here is my attempt to use Shovel (Rake, for Python) in Django.

Shovel can be used as an alternative to Django built-in Command. The reasons to use Shovel instead of the Command are:

1. "Rake, for Python" sounds cool.
2. Shovel is light-weight.
3. I can find all tasks in one place (the shovel/ directory).
4. I hate writing a list of make_option.
5. I hate inheriting LabelCommand, BaseCommand, NoArgsCommand, etc.

Okay, you get it... The reasons to use Shovel are actually: (i) "Rake, for Python" sounds cool, and (ii) I am lazy.

I didn't use the term "replacement for Django Command" because we cannot simply invoke Shovel task in the Django codebase using django.core.management.call_command(). (But we can have work-around, like making a Command to proxy the call)

Let's get back to my attempt to mix the two. I placed the shovel/ folder inside the Django project.

djangoproject/
  - manage.py
  - settings.py
  - urls.py
  - shovel/ 

And I setup the Django environment at the top of the Shovel task file.
try: # Load the django environment
    import imp
    import os
    import sys

    me = os.path.abspath(os.path.dirname(__file__))
    module_info = imp.find_module('context', [me])
    imp.load_module('context', *module_info)
except:
    print >> sys.stderr, 'Cannot setup Python environment from context.py'
At last, the setup injects a directory to Python sys.path and use Django function to load the settings.py.
def setup_django_env(path):
    from django.core.management import setup_environ
    try:
        module_info = imp.find_module('settings', [path])
        settings = imp.load_module('settings', *module_info)

        setup_environ(settings)
    except ImportError:
        msg = "Error: Can't find 'settings.py' in configured PYTHON_PATH", path
        print >> sys.stderr, msg
        sys.exit(1)

# assume shovel/ directory is placed at the same level of settings.py
setup_django_env(os.getcwd())
This is a common technique to integrate Django with other Python gears as well. By applying this technique, I can freely use any Django functions / models in Shovel.

NOTE 1: The name of Shovel task file cannot collide with any module/app name of the Django project.

NOTE 2: We can place the shovel/ folder outside the Django project but we have to use proper Python path and import statement (e.g. use `from themix.things.models import Thing` instead of `from things.models import Thing`).

My attempt can be found at - https://github.com/mrkschan/shovel-django-mix.
 
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