[ python-Bugs-1548371 ] filterwarnings('error') has no effect

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Bugs item #1548371, was opened at 2006-08-29 02:27
Message generated for change (Comment added) made by rupole
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Category: None
Group: Python 2.5
Status: Open
Resolution: None
Priority: 5
Submitted By: Roger Upole (rupole)
Assigned to: Nobody/Anonymous (nobody)
Summary: filterwarnings('error') has no effect

Initial Comment:
Once a warning has already been issued, 
warnings.filterwarnings('error',...) will not cause an 
error to be raised.  When the attached script is run, 
the warning is printed the first time thru the loop, 
but no error is raised the 2nd time thru.  Likewise, 
warnings.filterwarnings('always',...) will not cause 
the warning to be printed again.



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>Comment By: Roger Upole (rupole)
Date: 2006-08-31 23:38

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It might be simpler to check if the warning is in the line 
cache after the disposition is determined from the filters.
In the case of 'always' and 'error', there's no need to 
check the cache at all.


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Comment By: Marien Zwart (marienz)
Date: 2006-08-31 15:34

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This is caused by the warnings module caching when a
combination of message, Warning subclass and linenumber gets
ignored and bypassing the search through the warning filters
when that same combination occurs again.

I think it is possible to avoid this problem while keeping
the cache by keeping track of the "version" of the filters
list (a simple integer that is incremented every time the
filters list is modified through the functions in the
warnings module) and including this in the key tuple
warn_explicit uses to remember previous ignores. Old stuff
would remain in the cache but that should not be a big
problem (changes to the filters list should not be that common).

Does this sound reasonable? If it does I'll see if I can
produce a patch.

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