Serhiy Storchaka added the comment: Actually this wording is not quite correct. __setstate__() is called for any pickled state. It is not called only if the state is not pickled. The state is not pickled if reducing method (__reduce_ex__ or __reduce__) doesn't return state or returns None as a state. Default reducing method for protocol 0 and 1 doesn't return a state if __getstate__() returns false value. There are many other details of pickle protocol that are not correctly documented in the documentation of the pickle module. PEP 307 documents pickle protocol more correctly. ---------- nosy: +serhiy.storchaka _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue12290> _______________________________________