Import a class or function by name.

def _import_symbol(import_path, setting_name):
    """
    Import a class or function by name.
    """
    mod_name, class_name = import_path.rsplit('.', 1)

    # import module
    try:
        mod = import_module(mod_name)
        cls = getattr(mod, class_name)
    except ImportError as e:
        __, __, exc_traceback = sys.exc_info()
        frames = traceback.extract_tb(exc_traceback)
        if len(frames) > 1:
            raise   # import error is a level deeper.

        raise ImproperlyConfigured("{0} does not point to an existing class: {1}".format(setting_name, import_path))
    except AttributeError:
        raise ImproperlyConfigured("{0} does not point to an existing class: {1}".format(setting_name, import_path))

    return cls