FIX _get_items_to_delete raising error when items list empty

[Dr-Blank]

when calling .reduce_size on a newly created memory object without any cached items, it raises a ValueError: min() arg is an empty sequence. The argument of age_limit must not be None for this case.

Fixed by providing a default value to the min function used in calculating the oldest item, which would be the current datetime as no items exist.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (05caf07) 94.99% compared to head (4bfa65a) 94.95%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1503      +/-   ##
==========================================
- Coverage   94.99%   94.95%   -0.04%     
==========================================
  Files          45       45              
  Lines        7551     7556       +5     
==========================================
+ Hits         7173     7175       +2     
- Misses        378      381       +3     

Files	Coverage Δ
joblib/_store_backends.py	92.09% <100.00%> (-0.87%)	⬇️
joblib/test/test_memory.py	98.52% <100.00%> (+<0.01%)	⬆️

... and 1 file with indirect coverage changes

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[tomMoral]

thanks a lot for the pr.!

maybe a simpler solution is to skip the function of no item is present?

also could you add a non regression test for this case?

[Dr-Blank]

Thank you for your comment! 🚀

also could you add a non regression test for this case?

I would certainly like to try it.

Full disclosure:
I am a beginner programmer and would love to attempt this, however at the time of reading I do not understand what regression tests mean 😅

[tomMoral]

A non-regression test is a test case in test_memory.py, that checks that calling reduce_size on an empty memory object and verify that it does not crash.

I agree that the simpler is to skip the function when the items list is empty.

[tomMoral]

LGTM! thanks for the PR @Dr-Blank !

[fcharras]

There's a test that failed on last merge on main related to reduce size and age limit on windows: https://dev.azure.com/joblib/joblib/_build/results?buildId=3725&view=logs&j=8008bb8c-6b4f-56d5-66f4-b1d037aba1bf&t=7af8808d-3494-56e0-c1dc-6fbf5bb2bc40&l=1563

Could it be related to those changes ?

(edit: doesn't seem likely)

[gothicVI]

Can we please get this sorted out and merged?

It's a pain running with the following construct:

from datetime import timedelta
from joblib import Memory

cache_dir: Memory = Memory("/tmp/")  # nosec
try:
    cache_dir.reduce_size(age_limit=timedelta(days=1))
except ValueError:
    # https://github.com/joblib/joblib/pull/1503
    @cache_dir.cache(verbose=0)
    def dummy():
        """Define dummy function to initialize the cache."""

    dummy()
    cache_dir.reduce_size(age_limit=timedelta(days=1))

# define cached functions