Adding a little try/except/else block to the code above in the predicted spot
works. However the @etag value returned as part of the json payload doesn't have
the content-encoding suffix.

I claim this is not an issue as:

  the @etag value in the payload is not used by caches, proxies or other HTTP level
     transit nodes

  using the un-suffixed etag in an HTTP conditional header will (doesn't at the moment)
     still work and allow the change. This is fine as the use of etag in this case
     still works to prevent the lost update problem.

so I m not going to update the value of the payload's @etag value.