Error pickling SimpleLazyObject

[Iru Hwang <iru@…>]

Pickling SimpleLazyObject doesn't seem to work.
I've noticed that new classmethod "newobj" is added in 1.5 but seems it prevents the object from pickling.
This affects some cases when request.user needs to be pickled.

>>> from django.utils.functional import SimpleLazyObject
>>> from django.contrib.auth.models import User
>>> u = User.objects.all()[0]
>>> s = SimpleLazyObject(lambda: u)
>>> import pickle
>>> pickle.dumps(s)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/pickle.py", line 1374, in dumps
    Pickler(file, protocol).dump(obj)
  File "/usr/lib/python2.7/pickle.py", line 224, in dump
    self.save(obj)
  File "/usr/lib/python2.7/pickle.py", line 331, in save
    self.save_reduce(obj=obj, *rv)
  File "/usr/lib/python2.7/pickle.py", line 400, in save_reduce
    save(func)
  File "/usr/lib/python2.7/pickle.py", line 306, in save
    rv = reduce(self.proto)
  File "/usr/lib/python2.7/copy_reg.py", line 70, in _reduce_ex
    raise TypeError, "can't pickle %s objects" % base.__name__
TypeError: can't pickle instancemethod objects
>>> 

[Baptiste Mispelon]

I can reproduce the reported issue. And it is indeed a regression (the code in the report works in 1.4).

I traced the error to the following commit: b430e1db5f26d1de3a5cd0d6eae18603070fdab4

The attached patch is not valid however because it does not work with python3.

Some regression tests will also need to be included.

[Iru Hwang <iru@…>]

also checked the object is not compatible with cPickle.

>>> u = User.objects.all()[0]
>>> s = SimpleLazyObject(lambda: u)
>>> import cPickle
>>> cPickle.dumps(s)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: expected string or Unicode object, NoneType found

[Simon Charette]

Marking as Release blocker since this has been identifier as a regression from 1.4 to 1.5.

[Iru Hwang]

in python 2.x, pickle uses protocol 0 if it is not specified. (in 3.3 it uses 3 as default which is defined as pickle.DEFAULT_PROTOCOL)

​http://docs.python.org/2/library/pickle.html#data-stream-format

pickle.dumps({'method':method, 'arg':arg}, -1)
    or
pickle.dumps({'method':method, 'arg':arg}, pickle.HIGHEST_PROTOCOL)

This solves the problem so I don't think this is a blocker issue.

[Iru Hwang]

sorry for make you guys confused ;) can we close this? or is django code still need to be checked?

[Daniel Lindsley <daniel@…>]

In e24d486fbc0b1c42abe8b54217ff428e449c48cc:

Fixed #20212 - reduce should only be defined for Py3+.

[Daniel Lindsley <daniel@…>]

In cb9aaac91fb41b29b3d0d94f3cd208123c02a2ca:

[1.5.x] Fixed #20212 - reduce should only be defined for Py3+.