Python: capturing, hiding, and reporting warnings

I am sure you have already seen warnings coming from some Python code. I espcially encountered warnings about using deprecated features.

This always raises threww questions:

How can I hide the warnings?

How can I capture, collect, and report the warnings?

How can you create my own warnings?

Generate warnings

examples/python/warn.py

import warnings

def do_something():
    warnings.warn("Some warning")

def main():
    print("before")
    do_something()
    print("after")

main()

before
warn.py:4: UserWarning: Some warning
  warnings.warn("Some warning")
after

Capture and hide or print warnings

examples/python/warn_capture.py

import warnings

def do_something():
    warnings.warn("Some warning")
    warnings.warn("Other warning")

def main():
    print("before")
    with warnings.catch_warnings(record=True) as caught_warnings:
        warnings.simplefilter("always")
        do_something()
        for warn in caught_warnings:
            print("-----")
            print(f"warn: {warn.message}")
            print(warn.category)
            print(str(warn))
    print("-----")
    print("after")

main()

before
-----
warn: Some warning
<class 'UserWarning'>
{message : UserWarning('Some warning'), category : 'UserWarning', filename : 'warn_capture.py', lineno : 4, line : None}
-----
warn: Other warning
<class 'UserWarning'>
{message : UserWarning('Other warning'), category : 'UserWarning', filename : 'warn_capture.py', lineno : 5, line : None}
-----
after

Log the warnings

examples/python/warn_to_logger.py

import warnings
import logging

def do_something():
    warnings.warn("Some warning")

def main():
    logger = logging.getLogger('py.warnings')
    logging.captureWarnings(True)
    sh = logging.StreamHandler()
    sh.setLevel(logging.DEBUG)
    sh.setFormatter(logging.Formatter('%(asctime)s - %(levelname)-10s - %(message)s'))
    logger.addHandler(sh)

    logger.setLevel(logging.DEBUG)
    logger.info("before")
    do_something()
    logger.info("after")

main()

2020-06-27 09:41:37,847 - INFO       - before
2020-06-27 09:41:37,848 - WARNING    - warn_to_logger.py:5: UserWarning: Some warning
  warnings.warn("Some warning")

2020-06-27 09:41:37,848 - INFO       - after