So you want your stdout, stderr and logs in a file, but you only know the final log file name somewhere down the road?

name_changing_stream.py

"""
So you want your stdout, stderr and logs in a file, but you only know the final log file name somewhere down the road?
"""
import io
import sys
import threading
from pathlib import Path
from typing import IO, cast


class NameChangingStream(io.TextIOBase):
    def __init__(self, initial_path: Path):
        self.buffer = initial_path.open('w')
        self.lock = threading.RLock()

    def change_name(self, final_path: Path):
        assert self.lock, 'change_name() called twice'
        self.lock.acquire()
        self.buffer.flush()
        self.buffer.close()
        final_path = Path(self.buffer.buffer.raw.name).replace(final_path)
        self.buffer = final_path.open('a')
        self.lock.release()
        self.lock = None

    def write(self, s):
        if self.lock:
            self.lock.acquire()
            self.buffer.write(s)
            self.lock.release()
        else:
            self.buffer.write(s)


def test_usage():
    stream = cast(IO, NameChangingStream(Path('initial.log')))  # https://youtrack.jetbrains.com/issue/PY-23288
    sys.stdout = sys.stderr = stream

    import logging
    logger = logging.getLogger()
    logger.setLevel(logging.DEBUG)
    assert not logger.handlers
    handler = logging.StreamHandler(stream)
    formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
    handler.setFormatter(formatter)
    logger.addHandler(handler)

    logger.info('Hello')
    logger.info('World')

    if isinstance(stream, NameChangingStream):
        stream.change_name(Path('final.log'))

    logger.debug('Hello')
    logger.debug('World')
    print('FooBar')

    assert False, 'Goes to Log!'


test_usage()