python - Logging hierarchy vs. root logger?

Question

Somewhere in the bowels of my code I have something like:

logger = logging.getLogger('debug0.x')

The way I understand it, this should only respond when I have previously done something like:

logging.basicConfig(filename='10Nov2010a.txt',level=logging.DEBUG, name='debug0')

note that name has been defined as debug0. However, I have discovered that if do

logging.basicConfig(filename='10Nov2010a.txt',level=logging.DEBUG)

without the name keyword, then the debug0.x logger defined above reacts, and writes to the log file. I was thinking it would only react in the first case, when the logger had been named.

I'm confused.

Answer 1

The Python logging module organizes loggers in a hierarchy. All loggers are descendants of the root logger. Each logger passes log messages on to its parent.

New loggers are created with the getLogger() function. The function call logging.getLogger('debug0.x') creates a logger x which is a child of debug0 which itself is a child of the root logger. When logging to this logger, it will pass on the message to its parent, and its parent will pass the message to the root logger. You configured the root logger to log to a file by the basicConfig() function, so your message will end up there.