RotatingFileHandler throws an exception when delay

Question

When I run the following code under Python 2.6

import logging
from logging.handlers import RotatingFileHandler

rfh = RotatingFileHandler("testing.log", delay=True)
logging.getLogger().addHandler(rfh)
logging.warning("Boo!")

then the last line throws AttributeError: RotatingFileHandler instance has no attribute 'level'. So I add the line

rfh.setLevel(logging.DEBUG)

before the call to addHandler, and then the last line throws AttributeError: RotatingFileHandler instance has no attribute 'filters'. So if I manually set filters to be an empty list, then it complains about not having the attribute lock, etc.

When I remove the delay=True to leave it as the default value of False as documented here, the problem completely goes away.

Am I missing something? How do I properly use the delay parameter of the RotatingFileHandler class?

EDIT: Upon further analysis (presented in my own answer below), this looks like a bug, but I can't find a bug report on this in the Python bug tracker, even trying different search terms, so I guess I'll report it.

However, if someone can locate the actual bug report, then I can avoid submitting a duplicate reporting and wasting the time of the Python developers. I'll hold off on reporting the bug for a few hours, and if someone posts an answer that has the current bug report, then I'll accept that answer for this question.

Answer 1

I think I've just figured this out:

So it looks like one of the parent __init__ methods somewhere up the class hierarchy isn't getting called when delay is set. Indeed, examining the source code to the file logging/__init__.py in my Python install, I see the following code in the FileHandler.__init__ method:

if delay:
    self.stream = None
else:
    stream = self._open()
    StreamHandler.__init__(self, stream)

It looks like the FileHandler.emit method checks for un-opened streams and finishes initialization when logging is performed:

if self.stream is None:
    stream = self._open()
    StreamHandler.__init__(self, stream)
StreamHandler.emit(self, record)

So the problem is that in the BaseRotatingHandler.emit method, the shouldRollover and doRollover methods are called before emit-ing the record. This causes methods to be called which themselves assumed that the __init__ process has completed.

This looks like a bug, so I'll report it as such if I can't find it having been already been reported.

Answer 2

I've investigated this issue: it was fixed in Python SVN r68829 dated 20 Jan, 2009. This was after the release of 2.6.1 but before the release of 2.6.2.

Please upgrade to Python 2.6.2, or a later version.

I've updated the bug you filed. BTW the original bug report filed was #5013, which you could have found by searching all issues (not just open ones) for RotatingFileHandler, like this (from this page).