Question

I’m subclassing FileHandler to write a handler that produces correct xml files (meaning, not while the program is running, only after finishing).

what I do is:

• create the file,
• write a prologue (a <Diag> element opening),
• each log record causes a <line /> element in the xml
• stop logging means write the </Diag> element closer.

it would be nice if the Logger.removeHandler would call some special callback in the handler being removed, but I can’t find any. maybe it’s not there…

Answer 1

Handlers are not notified when they are added or removed from loggers. Loggers use handlers, but handlers know nothing about loggers.

However, a handler has a close() method that is called at program exit by logging.shutdown() (registered with atexit), so you can add your logic there. Just remember to call the base implementation’s close() to ensure proper housekeeping:

class MyHandler(logging.Handler):

    def close(self):
       # Write XML epilog.
       # ...
       super(MyHandler, self).close()