code: def get_backend(backend_class=None):
      
      cache_name = '_backend_instance'
      if not hasattr(get_backend, cache_name):
          backend_class = backend_class or settings.ROUGHPAGES_BACKEND
          if isinstance(backend_class, basestring):
              module_path, class_name = backend_class.rsplit(".", 1)
              module = import_module(module_path)
              backend_class = getattr(module, class_name)
          setattr(get_backend, cache_name, backend_class())
      return getattr(get_backend, cache_name)
docs: Get backend instance
  
      If no `backend_class` is specified, the backend class is determined from
      the value of `settings.ROUGHPAGES_BACKEND`.
      `backend_class` can be a class object or dots separated python import path
  
      Returns:
          backend instance