gistfile1.py

"""Publish and detect reusable app requirements.

Problem
-------

Django projects use a lot of external apps, some of these has dependencies
to other apps, the usual way of disclosing these dependencies is by writing
a note in the distributions README::

    This application depends on django-tagging.
    To use x from your project add the following to settings.py::

        INSTALLED_APPS = ("tagging",
                          "x")

Regular python modules can list their dependencies in setup.py to have
them automatically resolved, wouldn't it be nice if we could do that with
INSTALLED_APPS requirements as well?

Proposed solution
-----------------

Every reusable app has a .app module, for application metadata.
This module lists the INSTALLED_APPS requirements in a variable
called "requirements":

    >>> requirements = ["django.contrib.auth", "registration", "tagging"]


Then in your project settings you use :func`get_requirements` to
resolve all dependencies:

    >>> INSTALLED_APPS = ("django.contrib.auth",
    ...                   "durian",
    ...                   "myapp1",
    ...                   "myapp2",
    ... )
    >>> from djangoapp.appmeta import get_requirements
    >>> INSTALLED_APPS += get_requirements(INSTALLED_APPS)

"""
import sys
from collections import deque


def get_requirements(installed_apps):
    requirements = set()
    stream = deque(installed_apps)

    while True:
        if not stream:
            break
        next_app = stream.pop()
        subreqs = get_app_requirements(next_app)
        requirements |= subreqs
        stream.extend(subreqs & requirements)

    return tuple(requirements)


def get_app_requirements(app_name):
    try:
        __import__("%s.app" % app_name, {}, {}, [''])
    except ImportError:
        return set()
    app_mod = sys.modules["%s.app" % app_name]
    
    return set(getattr(app_mod, "requirements", []))