def getDatabaseList(self,):
    try:
        parent = "projects/"+self._PROJECT_NAME + "/instances/" + self._INSTANCE_NAME
        response = self.service.projects().instances().databases().list(parent=parent).execute()
    except Exception, e:
        logging.info("Exception while getDatabaseList %s", e)
        return False
    return response

Exception while getDatabaseList <HttpError 403 when requesting https://spanner.googleapis.com/v1/projects/<projectName>/instances/<instanceName>/databases?alt=json&key=<APIKEY>

returned "Resource projects/<projectName>/instances/<instanceName> is missing IAM permission: spanner.databases.list.">