python logging filter limitation, looks intentional?

Chris Withers chris at
Wed Jan 18 16:02:33 EST 2012

On 17/01/2012 10:48, Vinay Sajip wrote:
>> From: Chris Withers<chris at>
>> How breaking code? Configuration, maybe, but I can't see anyone being upset
>> that filtering would begin working "the same as everything else".
>> This just feels like a bug...
> Well, it means that filters that don't get called now would get called - and that's a change in behaviour.

How about an option that defaults to "backwards compatibility mode" for 
Python 2.7, flipped the other way in 3.3?

> It's not a bug, because it's like that by design. I understand that you don't agree with that particular design decision, but it's out there now. What you're asking for isn't unreasonable, but not achievable without a change in behaviour.

See above ;-)

> I don't want people to have to code differently for Python 3.3 and for older versions.

I must stress again, we're talking about a configuration change, not a 
code change, given the massive changes people are going to have to make 
between 2 and 3 anyway, I don't think that's unreasonable...

> True, but as I said earlier, you can attach a filter to your handlers. It's rather unlikely that you would have more than half-a-dozen handlers (since handlers ~= potential audiences for log events),

Yeah, just feels a bit icky...

>> Both use cases are valid, and a DelegatingHandler just feels like a hack to work
>> around a deficiency in the framework...
> Rather, the approach I've taken is not to assume I'll meet everyone's needs out of the box, but that the right pieces are in place for people to use logging in useful ways in scenarios that I haven't thought of - which shortcomings might well be termed "deficiencies" according to your point of view - by deriving and overriding classes, or by composing using filters, or setting module-level flags.

A module-level flag would be ideal :-)



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