# Backward Compatibility¶

attrs has a very strong backward compatibility policy that is inspired by the policy of the Twisted framework.

Put simply, you shouldn’t ever be afraid to upgrade attrs if you’re only using its public APIs. If there will ever be a need to break compatibility, it will be announced in the Changelog and raise a DeprecationWarning for a year (if possible) before it’s finally really broken.

Warning

The structure of the attr.Attribute class is exempt from this rule. It will change in the future, but since it should be considered read-only, that shouldn’t matter.

However if you intend to build extensions on top of attrs you have to anticipate that.