like that??

output.txt

2015-09-22 23:06:52,617 INFO info 1
2015-09-22 23:06:52,617 INFO level 1: info 2
2015-09-22 23:06:52,617 INFO level 1: info 3
2015-09-22 23:06:52,617 INFO level 1:level 2: info 3
2015-09-22 23:06:52,618 INFO level 1: test 4
2015-09-22 23:06:52,618 INFO test 5
2015-09-22 23:06:52,618 INFO before function
2015-09-22 23:06:52,618 INFO in-function-func: doing something....
2015-09-22 23:06:52,618 INFO after function

PrefixLogger.py

import logging
import contextlib


class PrefixLogger(logging.getLoggerClass()):
    _prefix = []

    @contextlib.contextmanager
    def prefix_context(self, prefix):
        self._prefix.append(prefix)
        yield
        self._prefix.pop()

    def prefix_decorator(self, prefix):
        def decorator(f):
            def wrapper(*args, **kwargs):
                with self.prefix_context(prefix):
                    return f(*args, **kwargs)
                return f
            return wrapper
        return decorator

    def handle(self, record):
        if self._prefix:
            record.msg = '{0}: {1}'.format(':'.join(self._prefix), record.msg)
        super(PrefixLogger, self).handle(record)


logging.setLoggerClass(PrefixLogger)


def main():

    logger = logging.getLogger('logger')
    logger.setLevel(logging.DEBUG)

    stream = logging.StreamHandler()
    stream.setLevel(logging.DEBUG)
    stream.setFormatter(logging.Formatter("%(asctime)s %(levelname)s %(message)s"))
    logger.addHandler(stream)

    logger.info('info 1')
    with logger.prefix_context('level 1'):
        logger.info('info 2')
        logger.info('info 3')
        with logger.prefix_context('level 2'):
            logger.info('info 3')

        logger.info('test 4')

    logger.info('test 5')

    @logger.prefix_decorator('in-function-func')
    def func():
        logger.info('doing something....')

    logger.info('before function')
    func()
    logger.info('after function')


if __name__ == '__main__':
    main()