Python cPickle bug

cPickle-bug.py

import cPickle
import Cookie

c = Cookie.SimpleCookie()
c['abc'] = 'def'

unpickled_highest = cPickle.loads(cPickle.dumps(c, cPickle.HIGHEST_PROTOCOL))
unpickled_default = cPickle.loads(cPickle.dumps(c))

print "c['abc'].value                ", c['abc'].value
print "unpickled_default['abc'].value", unpickled_default['abc'].value
print "unpickled_highest['abc'].value", unpickled_highest['abc'].value

assert unpickled_default['abc'].value == c['abc'].value
assert unpickled_highest['abc'].value == c['abc'].value

http://bugs.python.org/issue826897

Ugly, generic fix:

import cPickle


def cpickle_dumps(obj):
    """
    pickle doesn't handle dict sub-classes when using HIGHEST_PROTOCOL, so
    we do some checks here to avoid bugs.

    We pickle using HIGHEST_PROTOCOL if obj is not a dict subclass, otherwise we
    just use protocol version 1.

    :see: http://bugs.python.org/issue826897
    :param obj: The object to pickle
    :return: The pickled version of obj
    """
    if isinstance(obj, dict):
        return cPickle.dumps(obj, 1)

    return cPickle.dumps(obj, cPickle.HIGHEST_PROTOCOL)