Some TODOs for joblib 0.12.2

We introduce joblib 0.12.2 in https://github.com/scikit-learn/scikit-learn/pull/11741, but there’re still some TODOs (open an issue for further discussion) (1) Circle CI is failing

Unexpected failing examples:
/home/circleci/project/examples/cluster/plot_feature_agglomeration_vs_univariate_selection.py failed leaving traceback:
Traceback (most recent call last):
  File "/home/circleci/project/examples/cluster/plot_feature_agglomeration_vs_univariate_selection.py", line 75, in <module>
    clf.fit(X, y)  # set the best parameters
  File "/home/circleci/project/sklearn/model_selection/_search.py", line 663, in fit
    cv.split(X, y, groups)))
  File "/home/circleci/project/sklearn/externals/joblib/parallel.py", line 981, in __call__
    if self.dispatch_one_batch(iterator):
  File "/home/circleci/project/sklearn/externals/joblib/parallel.py", line 818, in dispatch_one_batch
    self._pickle_cache)
  File "/home/circleci/project/sklearn/externals/joblib/parallel.py", line 253, in __init__
    self.items = list(iterator_slice)
  File "/home/circleci/project/sklearn/model_selection/_search.py", line 662, in <genexpr>
    for parameters, (train, test) in product(candidate_params,
  File "/home/circleci/project/sklearn/base.py", line 62, in clone
    new_object_params[name] = clone(param, safe=False)
  File "/home/circleci/project/sklearn/base.py", line 50, in clone
    return estimator_type([clone(e, safe=safe) for e in estimator])
  File "/home/circleci/project/sklearn/base.py", line 50, in <listcomp>
    return estimator_type([clone(e, safe=safe) for e in estimator])
  File "/home/circleci/project/sklearn/base.py", line 50, in clone
    return estimator_type([clone(e, safe=safe) for e in estimator])
  File "/home/circleci/project/sklearn/base.py", line 50, in <listcomp>
    return estimator_type([clone(e, safe=safe) for e in estimator])
  File "/home/circleci/project/sklearn/base.py", line 62, in clone
    new_object_params[name] = clone(param, safe=False)
  File "/home/circleci/project/sklearn/base.py", line 53, in clone
    return copy.deepcopy(estimator)
  File "/home/circleci/miniconda/envs/testenv/lib/python3.6/copy.py", line 180, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/home/circleci/miniconda/envs/testenv/lib/python3.6/copy.py", line 274, in _reconstruct
    y = func(*args)
  File "/home/circleci/project/sklearn/externals/joblib/memory.py", line 830, in __init__
    location, cachedir))
ValueError: You set both "location='/tmp/tmp1v2mgts1' and "cachedir=False". 'cachedir' has been deprecated in version 0.12 and will be removed in version 0.14.
Please only set "location='/tmp/tmp1v2mgts1'"


/home/circleci/project/examples/compose/plot_compare_reduction.py failed leaving traceback:
Traceback (most recent call last):
  File "/home/circleci/project/examples/compose/plot_compare_reduction.py", line 119, in <module>
    grid.fit(digits.data, digits.target)
  File "/home/circleci/project/sklearn/model_selection/_search.py", line 663, in fit
    cv.split(X, y, groups)))
  File "/home/circleci/project/sklearn/externals/joblib/parallel.py", line 981, in __call__
    if self.dispatch_one_batch(iterator):
  File "/home/circleci/project/sklearn/externals/joblib/parallel.py", line 818, in dispatch_one_batch
    self._pickle_cache)
  File "/home/circleci/project/sklearn/externals/joblib/parallel.py", line 253, in __init__
    self.items = list(iterator_slice)
  File "/home/circleci/project/sklearn/model_selection/_search.py", line 662, in <genexpr>
    for parameters, (train, test) in product(candidate_params,
  File "/home/circleci/project/sklearn/base.py", line 62, in clone
    new_object_params[name] = clone(param, safe=False)
  File "/home/circleci/project/sklearn/base.py", line 53, in clone
    return copy.deepcopy(estimator)
  File "/home/circleci/miniconda/envs/testenv/lib/python3.6/copy.py", line 180, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/home/circleci/miniconda/envs/testenv/lib/python3.6/copy.py", line 274, in _reconstruct
    y = func(*args)
  File "/home/circleci/project/sklearn/externals/joblib/memory.py", line 830, in __init__
    location, cachedir))
ValueError: You set both "location='/tmp/tmpa408j1cz' and "cachedir=False". 'cachedir' has been deprecated in version 0.12 and will be removed in version 0.14.
Please only set "location='/tmp/tmpa408j1cz'"

(2) We get many extra warnings in the examples e.g., UserWarning: 'n_jobs' > 1 does not have any effect when 'solver' is set to 'liblinear'. Got 'n_jobs' = None. (3) In the doc, we still have things like n_jobs : int, optional (default=1) (4) Maybe add some explanations about the difference between n_jobs=1 and n_jobs=None?

[qinhanmin2014]

revert n_jobs=1 in the code and the docs, but that would not work with custom joblib backends (initial motivation for this change), so I don’t think it’s a solution.

+1

set n_jobs=None also in the docs, and specify that it corresponds to 1 job in each docstring.

We’ve updated the glossary, so we can refer to the glossary like what we’ve done for random_state.

I prefer to update the doc accordingly, but I agree that this should not block the release.

[qinhanmin2014]

Closing given joblib 0.12.3.