Thank you for the patch. Ideally I'd like to see some tests with it. Specifically I think these two would be useful:
1) Test that request is signed correctly. You could use Google's example  for validation.
2) Test that signing is triggered when client and key is provided.
These may seem like very obvious things but providing tests will help assure that future changes will not accidentally break existing functionality. I can write up the tests myself but that would be no sooner than the next weekend.
Almost finished the tests (required a bit of refactoring), but I've noticed that I actually get 4 failures when running the current doctests (in get_address_components and get_formatted_address). Maybe the results from Google vary by location of request? Or maybe the results have just changed...