I'm writing a RESTful API in Flask. I can access URL parameters via the [Request Object](http://flask.pocoo.org/docs/0.10/quickstart/#the-request-object). What is the best way to validate the given URL parameters? 

For example:

```
/places?zip=97239 # This is a valid filter
/places?foo=bar   # This is not a valid filter, 404 response?

```

One solution is to search through `request.args` and compare each entry against a set of valid URL parameters. Is there a better way?

Thanks!