#27979 deprecate the attribute loss_function_ that accesses a Cython extension class in SGDClassifier and SGDOneClassSVM. Unfortunately, PassiveAggressiveClassifier also inherits the loss_function_ attribute from BaseSGDClassifier and this was overlooked in #27979.

Now, what do we do?

1. Proper deprecation cycle delaying Plan for SGD and SAGA loss function migration #28049 for another year.
2. Remove it with 1.6 anyway.
3. Add the loss function as python function in PassiveAggressiveClassifier only, deprecate and remove in 2 releases.