How to log Python warnings in a Django log file?

Question

I have a Django application that I am migrating from v1.8 to v1.10. In the process of doing this work, I ran my application via:

python -Wall manage.py runserver

Doing so causes a number of Python warnings to appear in my console. I'd like to have these warnings show up in my Django application log, so I can examine them later. I thought my application's log handler would catch these warnings, but it doesn't. The log handler looks like the following (as taken from settings.py):

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'formatters': {
        'verbose': {
            'format': "[%(asctime)s] %(levelname)s [%(name)s:%(lineno)s] %(message)s",
            'datefmt': "%d/%b/%Y %H:%M:%S"
        },
        'simple': {
            'format': '%(levelname)s %(message)s'
        },
    },
    'handlers': {
        'file': {
            'level': 'WARNING',
            'class': 'logging.FileHandler',
            'filename': 'myapp.log',
            'formatter': 'verbose'
        },
    },
    'loggers': {
        'django': {
            'handlers': ['file'],
            'propagate': True,
            'level': 'WARNING',
        },
        'myapp': {
            'handlers': ['file'],
            'level': 'WARNING',
        },
    }
}

How can I capture Python warnings (with -Wall) in my Django log for examination later?

Answer 1

The warnings shown in python -Wall manage.py <command> are generated using warnings module. In Python2.7 logging module documentation, they have a section showing how to integrate messages from warnings module to logging.

Add these to your settings file.

import logging
logging.captureWarnings(True)

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'formatters': {
        'verbose': {
            'format': "[%(asctime)s] %(levelname)s [%(name)s:%(lineno)s] %(message)s",
            'datefmt': "%d/%b/%Y %H:%M:%S"
        },
        'simple': {
            'format': '%(levelname)s %(message)s'
        },
    },
    'handlers': {
        'file': {
            'level': 'WARNING',
            'class': 'logging.FileHandler',
            'filename': 'myapp.log',
            'formatter': 'verbose'
        },
    },
    'loggers': {
        'django': {
            'handlers': ['file'],
            'propagate': True,
            'level': 'WARNING',
        },
        'myapp': {
            'handlers': ['file'],
            'level': 'WARNING',
        },
        'py.warnings': {
            'handlers': ['file'],
            'level': 'WARNING',
            'propagate': True
        }
    }
}

After adding it, try to run any manage.py command and you can see the warnings written to your myapp.log file.

This line instructs logging to capture the py.warnings warnings:

    logging.captureWarnings(True)

This instructs logging to route (in this example to the file handler) warnings from the py.warnings logger:

    'py.warnings': {
        'handlers': ['file'],
        'level': 'WARNING',
        'propagate': True
    }