'A string that identifies the view (e.g. \'path.to.view_function\' or
\'path.to.ClassBasedView\').'

@cached_property
def lookup_str(self):

    callback = self.callback
    while isinstance(callback, functools.partial):
        callback = callback.func
    if (not hasattr(callback, '__name__')):
        return ((callback.__module__ + '.') + callback.__class__.__name__)
    return ((callback.__module__ + '.') + callback.__qualname__)
