[Cython] Cython creates non-pickleable classes

[Serhiy Storchaka]

Sorry, I'm not very familiar with Cython, but it looks to me that Cython 
creates extension classes that can't be correctly copied and unpickled. 
Since default __reduce_ex__ implementation knows nothing about Cython 
class structure, it's result doesn't contain the state of the object. 
The object could be pickled, but unpickled object doesn't contain 
original values of fields, it is just non-initialized. In recent CPython 
releases was added new restrictions for pickling objects that can't be 
correctly unpickled. This had added incompatibility with Cython classes. 
Building some packages now is failed, because Cython makes a deep copy 
that actually doesn't work.

See for original changes and discussion about the regression: 
http://bugs.python.org/issue22995 .

Besides the fact of Cython regression, it looks to me, that Cython also 
needs to be fixed. It can be done either by generating default 
pickle-related methods (__getnewargs__/__getnewargs_ex__, or 
__getstate__ + __setstate__, or __reduce__/__reduce_ex__) for all Cython 
classes, or implementing pickling or deepcopying only for NameAssignment 
and like.