captureWarnings set to True doesn't capture warnings

Question

I would like to log all warnings. I thought that setting captureWarnings to True should do the trick, but it doesn’t. Code:

import logging
import warnings

from logging.handlers import RotatingFileHandler

logger_file_handler = RotatingFileHandler(u'./test.log')
logger_file_handler.setLevel(logging.DEBUG)

logging.captureWarnings(True)

logger = logging.getLogger(__name__)

logger.addHandler(logger_file_handler)
logger.setLevel(logging.DEBUG)

logger.info(u'Test')
warnings.warn(u'Warning test')

My expectation is that ‘Warning test’ should appear in test.log, but it doesn’t; only ‘Test’ is put in the log file.

How to capture all warnings and redirect them to the log file?

Asked By: LAdas

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Source

Answer 1

logging.captureWarnings is not using your logger. It uses a logger named 'py.warnings'. You will need to configure that logger to do what you want.

Answered By: user2357112

Answer 2

From the logging.captureWarnings documentation:

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.

You probably want something like this:

import logging
import warnings

from logging.handlers import RotatingFileHandler

logger_file_handler = RotatingFileHandler(u'test.log')
logger_file_handler.setLevel(logging.DEBUG)

logging.captureWarnings(True)

logger = logging.getLogger(__name__)
warnings_logger = logging.getLogger("py.warnings")

logger.addHandler(logger_file_handler)
logger.setLevel(logging.DEBUG)
warnings_logger.addHandler(logger_file_handler)

logger.info(u'Test')
warnings.warn(u'Warning test')

Hope it helps!

Answered By: cdonts

Answer 3

In an application codebase, instead of explicitly configuring the py.warnings logger as other answers here suggest, you instead can – and probably want to – configure the root logger. This will:

Log stuff from py.warnings (the logger that the captureWarnings integration logs with)
Log stuff from libraries that create their own logger and log to it
Allow you to directly log using the logging module functions like logging.info instead of making a logger object

The following simple demo logs your warning as you want it to:

import logging
import warnings

from logging.handlers import RotatingFileHandler

logger_file_handler = RotatingFileHandler(u'./test.log')
logger_file_handler.setLevel(logging.DEBUG)

logging.captureWarnings(True)

root_logger = logging.getLogger()

root_logger.addHandler(logger_file_handler)
root_logger.setLevel(logging.DEBUG)

logging.info(u'Test')
warnings.warn(u'Warning test')

Answered By: Mark Amery

Answer 4

Not directly relevant for the OP, but may be useful for others winding up here based on the title:

Another reason for warnings not to show up in your logs would be if you use warnings.catch_warnings with record=True.

Here’s a minimal example:

import logging
import warnings

logging.basicConfig()  # configures the root logger

logging.captureWarnings(True)

warnings.warn('logged')

with warnings.catch_warnings():
    warnings.warn('also logged')


with warnings.catch_warnings(record=True) as warnings_caught:
    warnings.warn('not logged')

# show warnings recorded
print([w.message for w in warnings_caught])

Answered By: djvg

captureWarnings set to True doesn't capture warnings

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