edan_f0/oscar/services.py

from exceptions import Exception
from imp import new_module

from django.conf import settings

class AppNotFoundError(Exception):
    pass

def import_module(mod_name, classes=[]):
    """
    For dynamically importing classes from a module based on the mapping within 
    settings.py
    
    Eg. calling import_module('product.models') will search INSTALLED_APPS for
    the relevant product app (default is 'oscar.product') and then import the
    classes from there.   
    
    We search the INSTALLED_APPS list to find the appropriate app string and 
    import that.
    
    This is very similar to django.db.models.get_model although that is only 
    for loading models while this method will load any class.
    """
    # Classes must be specified in order for __import__ to work correctly.  It's
    # also a good practice
    if not classes:
        raise ValueError("You must specify the classes to import")
    # Arguments will be things like 'product.models' and so we
    # we take the first component to find within the INSTALLED_APPS list.
    app_name = mod_name.split(".")[0]
    for installed_app in  settings.INSTALLED_APPS:
        installed_app_parts = installed_app.split(".")
        try: 
            # We search the second component of the installed apps
            if app_name == installed_app_parts[1]:
                real_app = "%s.%s" % (installed_app_parts[0], mod_name)
                # Passing classes to __import__ here does not actually filter out the 
                # classes, we need to iterate through and assign them individually.
                mod = new_module(real_app)
                imported_mod = __import__(real_app, fromlist=classes)
                for classname in classes:
                    mod.__setattr__(classname, getattr(imported_mod, classname))
                return mod
        except IndexError:
            pass
    raise AppNotFoundError("Unable to find an app matching %s in INSTALLED_APPS" % (app_name,))