code: def call_modules(auto_discover=()):
      
      for app in settings.INSTALLED_APPS:
          modules = set(auto_discover)
          if app in INSTALLED_APPS_REGISTER:
              modules.update(INSTALLED_APPS_REGISTER[app])
          for module in modules:
              mod = import_module(app)
              try:
                  import_module('%s.%s' % (app, module))
                  inst = getattr(mod, '__install__', lambda: None)
                  inst()
              except:
                  if module_has_submodule(mod, module):
                      raise
      app_modules_loaded.send(sender=None)
docs: this is called in project urls.py
      for registering desired modules (eg.: admin.py)