Configure python logging to stderr only

configure_logging_to_stderr_only.py

import logging
import os
import sys
from distutils.util import strtobool
from typing import Optional


def configure_logging_to_stderr_only(filename: Optional[str] = None):
    """Configures a basic config depending on 'DEBUG' env variable,
    and also re-configures all existing handlers to output to stderr
    (so that our program can solely use stdout).
    """
    logger = logging.getLogger(filename)
    kwargs = {}
    is_debug = bool(strtobool(os.environ.get("DEBUG") or "false"))
    kwargs["level"] = logging.DEBUG if is_debug else logging.INFO
    kwargs["stream"] = sys.stderr
    logging.basicConfig(**kwargs)

    # Resetting all existing handlers to stderr
    for logger_name in logging.root.manager.loggerDict:
        lgr = logging.getLogger(logger_name)
        for hdl in lgr.handlers:
            if isinstance(hdl, logging.StreamHandler) and hdl.stream != sys.stderr:
                lgr.removeHandler(hdl)
                hdl.setStream(sys.stderr)
                lgr.addHandler(hdl)
                logging.debug(f"Redirected log handler to stderr: {lgr.name}")

    return logger