def add_execution_event(self, context_id, event):
        """Within a context, append data to the execution result.

        Args:
            context_id (str): the context id returned by create_context
            data_type (str): type of data to append
            data (bytes): data to append

        Returns:
            (bool): True if the operation is successful, False if
                the context_id doesn't reference a known context.
        """
        if context_id not in self._contexts:
            LOGGER.warning("Context_id not in contexts, %s", context_id)
            return False

        context = self._contexts.get(context_id)
        context.add_execution_event(event)
        return True