I thought of that but there's annoying steps you have to take to make that work. There's no easy way to make a class attribute from a function (like `@property` does for instances) so i can't do something like

```python
@classproperty
@memoized
def param_url_map(cls):
    return {v:k for k, v in cls.url_param_map.iteritems()}
```

and if i do it with a simple `param_url_map = ...` assignment in the top level, then subclasses can't override this value. (You'd need a metaclass for that, which would be overkill and way less readable.) So, I figured this solution would work just fine and the method name is descriptive enough to make it clear what its intent is