ENH add cache_validation_callback in Memory

[tomMoral]

Tentative to implement a way to validate the cache results with user define rules.

• Add an argument validate_cache that takes a callable validate_cache(metadata) -> bool.
• Add time in metadata to ease the robust checking of computation time in all backends.
• Add an helper joblib.memory.expires_after to check the age of a cached results.
• Add some small tests
• Clean some leftover pep8 :)

Todo:

• Add some doc if the API is validated.
• Add some entry in changelog.

Fixes #313 .

[codecov]

Codecov Report

Patch coverage: 98.82% and project coverage change: +0.10 🎉

Comparison is base (9f7edc2) 94.82% compared to head (c06dc88) 94.93%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1149      +/-   ##
==========================================
+ Coverage   94.82%   94.93%   +0.10%     
==========================================
  Files          44       44              
  Lines        7366     7439      +73     
==========================================
+ Hits         6985     7062      +77     
+ Misses        381      377       -4     

Impacted Files	Coverage Δ
joblib/memory.py	95.42% <96.77%> (+0.23%)	⬆️
joblib/__init__.py	100.00% <100.00%> (ø)
joblib/test/test_memory.py	98.52% <100.00%> (+0.09%)	⬆️

... and 1 file with indirect coverage changes

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[tomMoral]

some improvements

[jjerphan]

Hi @tomMoral,

After some delay, here is a first superficial pass. I still need to get into MemorizedFunc's internals to see how everything fits together.

[tomMoral]

Thx for the review @jjerphan ! I did update this a bit. I will try to finish this by adding some examples and a bit of doc.

[jjerphan]

Thx for the review @jjerphan !

You're welcome.

I did update this a bit. I will try to finish this by adding some examples and a bit of doc.

Feel free to request a new review when it's ready.

[tomMoral]

@jjerphan I rebased the PR and did a pass on the doc, feel free to review once more :)

[jjerphan]

It looks like the tests are failing in some configurations.

I mostly am busy with other tasks now but will try to come back to it soon.

[jjerphan]

After discussing a few remark and changing this PR title to mention cache_validation_callback instead of validate_cache, this LGTM. 👍

[jjerphan]

My previous review might be outdated, let me know if you want another one, @tomMoral.

[xloem]

This popular feature appears to have rested unmerged after passing an extended review. Sadly there are now conflicts and test failures again. Is this good to merge if it is ported forward?

[tomMoral]

I just fixed this, I will try to merge it to include it in the next release.