You can use the HTTP error code from the exception. BigQuery is a REST API, so the response codes that are returned match the description of HTTP error codes here.
Here is some code that handles retryable errors (connection, rate limit, etc), but re-raises when it is an error type that it doesn't expect.
except HttpError, err:
# If the error is a rate limit or connection error, wait and
# try again.
# 403: Forbidden: Both access denied and rate limits.
# 408: Timeout
# 500: Internal Service Error
# 503: Service Unavailable
if err.resp.status in [403, 408, 500, 503]:
print '%s: Retryable error %s, waiting' % (
self.thread_id, err.resp.status,)
time.sleep(5)
else: raise
If you want even better error handling, check out the BigqueryError class in the bq command line client (this used to be available on code.google.com, but with the recent switch to gCloud, it isn't any more. But if you have gcloud installed, the bq.py and bigquery_client.py files should be in the installation).