Backward compatibility helper for write command error handling.

def _check_write_command_response(results):
    """Backward compatibility helper for write command error handling.
    """
    errors = [res for res in results
              if "writeErrors" in res[1] or "writeConcernError" in res[1]]
    if errors:
        # If multiple batches had errors
        # raise from the last batch.
        offset, result = errors[-1]
        # Prefer write errors over write concern errors
        write_errors = result.get("writeErrors")
        if write_errors:
            # If the last batch had multiple errors only report
            # the last error to emulate continue_on_error.
            error = write_errors[-1]
            error["index"] += offset
            if error.get("code") == 11000:
                raise DuplicateKeyError(error.get("errmsg"), 11000, error)
            raise WriteError(error.get("errmsg"), error.get("code"), error)
        else:
            error = result["writeConcernError"]
            if "errInfo" in error and error["errInfo"].get('wtimeout'):
                # Make sure we raise WTimeoutError
                raise WTimeoutError(
                    error.get("errmsg"), error.get("code"), error)
            raise WriteConcernError(
                error.get("errmsg"), error.get("code"), error)