Note: Python 2.7 has reached end of support on January 31, 2024. Your existing Python 2.7 applications will continue to run and receive traffic. However, App Engine might block re-deployment of applications that use runtimes after their end of support date. We recommend that you migrate to the latest supported version of Python.

Cloud Storage Errors and Error Handling

Google Cloud Storage is accessed by the App Engine UrlFetch feature. As a result, there are three sources of possible errors:

App Engine UrlFetch transient errors.
Google Cloud Storage transient errors.
Google Cloud Storage errors related to buckets and object authorization.

The App Engine client library for Cloud Storage handles timeout errors on both the App Engine side and the Google Cloud Storage side and performs retries automatically, so your app does not need to add logic to handle this. The configuration of the timeout and retry mechanism is exposed through the RetryParams class, which you can use to change any or all of the default settings. You can make your changes to apply to all function calls or you can specify changes for a specific call using the function's retry_params parameter.

Errors

The App Engine client library for Cloud Storage has the following error exception classes defined:

cloudstorage.Error

The base class for all exceptions in this package. Errors can be generated from App Engine or from Google Cloud Storage. For details on HTTP error codes from Google Cloud Storage, see HTTP Status and Error Codes in the Google Cloud Storage documentation.

cloudstorage.AuthorizationError

An unauthorized request was received by Google Cloud Storage. This error can occur if an authorized app is using an access token that has expired. Normally, this error is handled automatically in the App Engine client library for Cloud Storage, which gets a new access token and retries the request.

cloudstorage.ForbiddenError

This error (403) indicates that the user was not authorized by Google Cloud Storage to make the request.

The various possible causes for this error are listed in the Google Cloud Storage error documentation for 403-Forbidden.
A common source of this error is that the bucket permissions (bucket ACL) are not set properly to allow your app access. See Google Cloud Storage Authentication for information on setting up access.

cloudstorage.NotFoundError

HTTP error 404. The bucket or object you specified in a call to cloudstorage.delete(), cloudstorage.listbucket(), cloudstorage.open(), or cloudstorage.stat() does not exist.

cloudstorage.TimeoutError

This error is raised when the attempt to contact Google Cloud Storage servers times out even after retry attempts. (See RetryParams for information on changing the default timeout handling and retries.