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1. braingram

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Sep 26, 2025
2. picnixz commented on Sep 26, 2025

   

   picnixz

   on Sep 26, 2025

   Member

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   The docs say:

   If capture is True, warnings issued by the warnings module will be redirected to the logging system. Specifically, a warning will be formatted using warnings.formatwarning() and the resulting string logged to a logger named 'py.warnings' with a severity of WARNING.

   AFAIU, calling logging.captureWarnings(True) means that the first example works as intended (the responsibility for handling warnings is left to logging). For the second example, do you mean that we have both a logging warning and a non-logging warning? (from warnings)?

   Thus I don't know if it's a bug or a docs issue here.

   cc @vsajip
3. picnixz

   added

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   on Sep 26, 2025
4. picnixz

   added this to Logging issues 🪵on Sep 26, 2025
5. picnixz

   changed the title [-]enabling logging.captureWarnings inside warnings.catch_warnings causes warnings to not be recorded[/-] [+]`logging.captureWarnings` and `warnings.catch_warnings` do not play well together[/+] on Sep 26, 2025
6. braingram commented on Sep 26, 2025

   

   braingram

   on Sep 26, 2025

   Author

   More actions

   AFAIU, calling logging.captureWarnings(True) means that the first example works as intended (the responsibility for handling warnings is left to logging). For the second example, do you mean that we have both a logging warning and a non-logging warning? (from warnings)?

   There's no logging message in the second example:

   import logging, warnings
   logging.captureWarnings(True)
   with warnings.catch_warnings(record=True) as rec:
       warnings.warn("foo")
   assert len(rec) == 1

   for maybe 2 reasons. One is that the warning doesn't appear to "prime" the logging machinery (I'm not sure what's happening here). For this minimal example:

   import logging, warnings
   logging.captureWarnings(True)
   warnings.warn("foo")

   I see no log messages and no warning. However if I add a logging.warning:

   import logging, warnings
   logging.warning("bar")
   logging.captureWarnings(True)
   warnings.warn("foo")

   I now see 2 logging messages and a warning:

   WARNING:root:bar
   WARNING:py.warnings:...:...: UserWarning: foo
     warnings.warn("foo")
   

   If I then update the example adding the logging.warning:

   import logging, warnings
   logging.warning("bar")
   logging.captureWarnings(True)
   with warnings.catch_warnings(record=True) as rec:
       warnings.warn("foo")
   assert len(rec) == 1

   it shows only the added logging.warning message and no warning (but the assert passes). The output is:

   WARNING:root:bar
   

   which I think points to the 2nd reason the "foo" is not shown in the log or warned due to the catch_warnings doing what I think is expected here (catching and recording the warnings).

   Thanks for the documentation excerpt. To revisit this example:

   import logging, warnings
   logging.warning("bar")
   logging.captureWarnings(True)
   warnings.warn("foo")

   where 2 log messages are shown and 1 warning. I think this is the behavior I would expect where captureWarnings is allowing warnings to be logged but not preventing them from also being warnings.

   Maybe the fact that this producing no log and no warning is a separate bug?

   import logging, warnings
   logging.captureWarnings(True)
   warnings.warn("foo")