six.moves cannot be pickled with cloudpickle

[li-dan]

six.moves cannot be pickled with cloudpickle. Reproducer:

#!/usr/bin/env python
from __future__ import absolute_import, division, print_function

import cloudpickle
import six.moves

if __name__ == "__main__":
    print("cloudpickle version:", cloudpickle.__version__)
    print("six version:", six.__version__)
    cloudpickle.loads(cloudpickle.dumps(six.moves))

With Python version 2.7.11, cloudpickle version 0.2.2 and six version 1.10.0, this throws a RuntimeError with the message "maximum recursion depth exceeded while calling a Python object":

cloudpickle version: 0.2.2
six version: 1.10.0
Traceback (most recent call last):
  File "test.py", line 10, in <module>
    cloudpickle.loads(cloudpickle.dumps(six.moves))
  File "/opt/python/python-2.7/lib64/python2.7/pickle.py", line 1388, in loads
    return Unpickler(file).load()
  File "/opt/python/python-2.7/lib64/python2.7/pickle.py", line 864, in load
    dispatch[key](self)
  File "/opt/python/python-2.7/lib64/python2.7/pickle.py", line 1221, in load_build
    setstate = getattr(inst, "__setstate__", None)
  File "/usr/local/python/python-2.7/std/lib/python2.7/site-packages/six.py", line 118, in __getattr__
    _module = self._resolve()
  File "/usr/local/python/python-2.7/std/lib/python2.7/site-packages/six.py", line 115, in _resolve
    return _import_module(self.mod)
...

The reason for pickling six.moves is that a recent commit to cloudpickle changed it to pickle any modules that are used by functions, so pickling a function will also pickle any modules that it uses. For example, the bug is triggered by:

#!/usr/bin/env python
from __future__ import absolute_import, division, print_function

import cloudpickle
import six.moves

def f():
    C = six.moves.http_cookies.SimpleCookie()
    return C

if __name__ == "__main__":
    cloudpickle.loads(cloudpickle.dumps(f))

I think the issue can be fixed by defining _LazyModule.__reduce__:

def __reduce__(self):
    return _import_module, (self.__name__,)