Shade Developer Coding Standards

Shade Developer Coding Standards

In the beginning, there were no guidelines. And it was good. But that didn’t last long. As more and more people added more and more code, we realized that we needed a set of coding standards to make sure that the shade API at least attempted to display some form of consistency.

Thus, these coding standards/guidelines were developed. Note that not all of shade adheres to these standards just yet. Some older code has not been updated because we need to maintain backward compatibility. Some of it just hasn’t been changed yet. But be clear, all new code must adhere to these guidelines.

Below are the patterns that we expect Shade developers to follow.

Release Notes

Shade uses reno for managing its release notes. A new release note should be added to your contribution anytime you add new API calls, fix significant bugs, add new functionality or parameters to existing API calls, or make any other significant changes to the code base that we should draw attention to for the user base.

It is not necessary to add release notes for minor fixes, such as correction of documentation typos, minor code cleanup or reorganization, or any other change that a user would not notice through normal usage.

API Methods

  • When an API call acts on a resource that has both a unique ID and a name, that API call should accept either identifier with a name_or_id parameter.

  • All resources should adhere to the get/list/search interface that control retrieval of those resources. E.g., get_image(), list_images(), search_images().

  • Resources should have create_RESOURCE(), delete_RESOURCE(), update_RESOURCE() API methods (as it makes sense).

  • For those methods that should behave differently for omitted or None-valued parameters, use the _utils.valid_kwargs decorator. Notably: all Neutron update_* functions.

  • Deleting a resource should return True if the delete succeeded, or False if the resource was not found.


All underlying client exceptions must be captured and converted to an OpenStackCloudException or one of its derivatives.

REST Calls

All interactions with the cloud should be done with direct REST using the appropriate keystoneauth1.adapter.Adapter. See Glance and Swift calls for examples.

Returned Resources

Complex objects returned to the caller must be a munch.Munch type. The shade._adapter.Adapter class makes resources into munch.Munch.

All objects should be normalized. It is shade’s purpose in life to make OpenStack consistent for end users, and this means not trusting the clouds to return consistent objects. There should be a normalize function in shade/ that is applied to objects before returning them to the user. See Data Model for further details on object model requirements.

Fields should not be in the normalization contract if we cannot commit to providing them to all users.

Fields should be renamed in normalization to be consistent with the rest of shade. For instance, nothing in shade exposes the legacy OpenStack concept of “tenant” to a user, but instead uses “project” even if the cloud uses tenant.

Nova vs. Neutron

  • Recognize that not all cloud providers support Neutron, so never assume it will be present. If a task can be handled by either Neutron or Nova, code it to be handled by either.

  • For methods that accept either a Nova pool or Neutron network, the parameter should just refer to the network, but documentation of it should explain about the pool. See: create_floating_ip() and available_floating_ip() methods.


  • New API methods must have unit tests!

  • New unit tests should only mock at the REST layer using requests_mock. Any mocking of shade itself or of legacy client libraries should be considered legacy and to be avoided.

  • Functional tests should be added, when possible.

  • In functional tests, always use unique names (for resources that have this attribute) and use it for clean up (see next point).

  • In functional tests, always define cleanup functions to delete data added by your test, should something go wrong. Data removal should be wrapped in a try except block and try to delete as many entries added by the test as possible.

Creative Commons Attribution 3.0 License

Except where otherwise noted, this document is licensed under Creative Commons Attribution 3.0 License. See all OpenStack Legal Documents.