My reactions to Python's warnings module

April 14, 2014

A commentator on my entry on the warnings problem pointed out the existence of the warnings module as a possible solution to my issue. I've now played around with it and I don't think it fits my needs here, for two somewhat related reasons.

The first reason is that it simply makes me nervous to use or even take over the same infrastructure that Python itself uses for things like deprecation warnings. Warnings produced about Python code and warnings that my code produces are completely separate things and I don't like mingling them together, partly because they have significantly different needs.

The second reason is that the default formatting that the warnings module uses is completely wrong for the 'warnings produced from my program' case. I want my program warnings to produce standard Unix format (warning) messages and to, for example, not include the Python code snippet that generated them. Based on playing around with the warnings module briefly it's fairly clear that I would have to significantly reformat standard warnings to do what I want. At that point I'm not getting much out of the warnings module itself.

All of this is a sign of a fundamental decision in the warnings module: the warnings module is only designed to produce warnings about Python code. This core design purpose is reflected in many ways throughout the module, such as in the various sorts of filtering it offers and how you can't actually change the output format as far as I can see. I think that this makes it a bad fit for anything except that core purpose.

In short, if I want to log warnings I'm better off using general logging and general log filtering to control what warnings get printed. What features I want there are another entry.

Written on 14 April 2014.
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Last modified: Mon Apr 14 01:19:06 2014
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