Cannot pickle properties with python 3.8

[mhooreman]

Hello,

The following code, which uses joblib with cloudpickle backend, crashes with python 3.8.1, but works with python 3.7.4. Can you fix it?

Thanks

Python code:

import joblib as jl

class Test:
    def __init__(self, a):
        self._a = a 

    @property 
    def a(self): 
        return self._a 


def jlcb(x):
    Test(x).a

jl.Parallel(n_jobs=-1)(jl.delayed(jlcb)(z) for z in range(100))

Exception with python 3.8.1 (paths partially replaced with "#########")

joblib.externals.loky.process_executor._RemoteTraceback: 
"""
Traceback (most recent call last):
  File "#########/.local/share/virtualenvs/3.8-tCZLdKH5/lib/python3.8/site-packages/joblib/externals/loky/backend/queues.py", line 150, in _feed
    obj_ = dumps(obj, reducers=reducers)
  File "#########/.local/share/virtualenvs/3.8-tCZLdKH5/lib/python3.8/site-packages/joblib/externals/loky/backend/reduction.py", line 247, in dumps
    dump(obj, buf, reducers=reducers, protocol=protocol)
  File "#########/.local/share/virtualenvs/3.8-tCZLdKH5/lib/python3.8/site-packages/joblib/externals/loky/backend/reduction.py", line 240, in dump
    _LokyPickler(file, reducers=reducers, protocol=protocol).dump(obj)
  File "#########/.local/share/virtualenvs/3.8-tCZLdKH5/lib/python3.8/site-packages/joblib/externals/cloudpickle/cloudpickle_fast.py", line 538, in dump
    return Pickler.dump(self, obj)
TypeError: cannot pickle 'property' object
"""

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "../demo_joblib.py", line 15, in <module>
    jl.Parallel(n_jobs=-1)(jl.delayed(jlcb)(z) for z in range(100))
  File "#########/.local/share/virtualenvs/3.8-tCZLdKH5/lib/python3.8/site-packages/joblib/parallel.py", line 1017, in __call__
    self.retrieve()
  File "#########/.local/share/virtualenvs/3.8-tCZLdKH5/lib/python3.8/site-packages/joblib/parallel.py", line 909, in retrieve
    self._output.extend(job.get(timeout=self.timeout))
  File "#########/.local/share/virtualenvs/3.8-tCZLdKH5/lib/python3.8/site-packages/joblib/_parallel_backends.py", line 562, in wrap_future_result
    return future.result(timeout=timeout)
  File "/opt/python/3.8.1/lib/python3.8/concurrent/futures/_base.py", line 439, in result
    return self.__get_result()
  File "/opt/python/3.8.1/lib/python3.8/concurrent/futures/_base.py", line 388, in __get_result
    raise self._exception
_pickle.PicklingError: Could not pickle the task to send it to the workers.

[pierreglaser]

Thanks for reporting. Will investigate.

[mhooreman]

Thanks a lot @ogrisel and @Lingepumpe