重复的日志输出,但没有重复的处理程序

我如何调试这个?

import io
import logging
import os
import sys
from typing import Optional


DEFAULT_LOG_LEVEL = logging.INFO


def get_sub_loggers():
    return [
        logging.getLogger('a'),
        logging.getLogger('b'),
        logging.getLogger('c')
    ]


def safe_add_handler(logger: logging.Logger, h: logging.Handler) -> None:
    if h not in logger.handlers:
        logger.addHandler(h)


def safe_add_filter(logger: logging.Logger, f: logging.Filter) -> None:
    if f not in logger.filters:
        logger.addFilter(f)


def configure_logging(main_logger: logging.Logger,
                      log_level = DEFAULT_LOG_LEVEL,
                      log_file = None,
                      fmt: Optional[str] = None,
                      force_add_handler: bool = False) -> None:
    main_logger.setLevel(log_level)
    logging.captureWarnings(True)  # send all warnings to be logged

    if force_add_handler or not main_logger.hasHandlers():
        if log_file is None or log_file == '-':
            log_file = sys.stderr

        if isinstance(log_file, (str, os.PathLike)):
            handler = logging.FileHandler(log_file)
        else:
            handler = logging.StreamHandler(log_file)

        handler.setFormatter(logging.Formatter(fmt if fmt is not None else logging.BASIC_FORMAT))

        main_logger.addHandler(handler)
        log_output_location = handler.stream.name if isinstance(handler, logging.StreamHandler) else handler.baseFilename
        main_logger.info('Writing logs to {}'.format(log_output_location))
    else:
        main_logger.info('Using existing log handlers')

    main_logger.info('Using log level {}'.format(log_level))

    for logger in get_sub_loggers():
        logger.setLevel(log_level)
        for h in main_logger.handlers:
            safe_add_handler(logger, h)
        for f in main_logger.filters:
            safe_add_filter(logger, f)
        main_logger.debug('Configured logger {}'.format(logger.name))

    main_logger.info('Configured submodule loggers.')


configure_logging(logging.getLogger())

a_logger = logging.getLogger('a')
assert len(a_logger.handlers) == 1

# Should only output "hi" once, but it does it twice
a_logger.info('hi')