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warnings: warning filters with action="once" do not honor regex wildcards #153129
Description
Activity
For me, the definition
"once": A warning is considered a repeat if the (message, category) are the same, ignoring the module and line number.
is the correct one. It just means that you are "action='once'" + pattern would simply mean that you are trying to catch that specific message using that pattern and that you only want it once afterwards. In particular, I believe that:
warnings.filterwarnings("once", "test warning.*", UserWarning) warnings.warn("test warning 1", UserWarning) warnings.warn("test warning 2", UserWarning) warnings.warn("test warning 1", UserWarning) # doesn't show
is correct. Using a pattern is a way to add a "once" filter for all messages that could start with a given prefix.
Reacted by Serhiy StorchakaThat's a fair assessment. I can see how that would be the desired behavior in a lot of cases.
In my particular use case, honoring the regex was what I had intended, and then found it surprising that it didn't work. Re-reading with added context, I can see how even the first statement about "once" behavior could be interpreted to say that it is tracking instances of string literal messages - so there isn't necessarily even a documentation discrepancy.
It could be nice to have a feature which allows for the more generic regex interpretation of once tracking, but I suspect that would be a disproportionate amount of work relative to the benefit it provides.
Yes I do not think we want to make that feature so I will close it as
not planned
Bug report
Bug description:
When a warning filter is applied with
action="once"and amessageregex pattern using wildcards, the wild card is not honored when determining if a warning has already been output. The messages are compared as string literals to assess whether a warning has already been output.For example, the following code results in two warning outputs:
The
warningsmodule documentation (referencing 3.14.6 documentation at time of writing) is somewhat ambiguous on how wildcards are interpreted foraction="once". There are a couple mentions of expected behavior:The former seems to imply pattern matching (i.e. the code example above would only output 1 warning), whereas the latter implies string literal comparison.
Potential remedies:
action="once"Path #2 seems like the more useful route from a user perspective.
CPython versions tested on:
3.14
Operating systems tested on:
Linux