I've added an xisbn [1] response to isbn queries against OPA [2]. The updated opa.py is attached; see earlier posts for the rest of the whole package.

Sample links:

• http://opa.onebiglibrary.net/?id=urn:isbn:1565923928 [3]
• http://opa.onebiglibrary.net/?id=urn:isbn:1565923928&format=xisbn [4]

Note that neither this nor the earlier update is redirecting properly, rather they are republishing the remote data. This is a bug needing fixing, but that will have to wait for a full refactoring. (Hmm, that would be a good project during the upcoming code4lib conference...)