[Twisted-Python] the good, the log, and the ugly

Glyph glyph at twistedmatrix.com
Mon Mar 26 16:02:34 EDT 2012

On Mar 26, 2012, at 10:38 AM, exarkun at twistedmatrix.com wrote:

> I agree with just about everything here, except I think we should be 
> able to do better than the `format="opaque string"´ part.

In principle I agree, but I'm not sure about how to do that _exactly now_.  Whereas today, immediately, all log messages could be written in the style I suggested and it would be a big improvement.

> Logging in the style you outlined here preserves the structure of the 
> information, but it omits any consistent way to identify what the 
> structure is.  It seems to leave only two possibilities:
>  - Compare the format string to certain well-known format strings and 
> use a match (if found) to make decisions based on a priori knowledge 
> about the additional items in the log event.

Previous (limited) experience with internationalization efforts lead me to believe that looking at well-known format strings to determine meaning is the state of the art.

>  - Compare the set of keys in the log event to certain well-known sets 
> and use a match there to make the same kind of decision.
> Neither of these sounds like a good thing.

Still, a pretty substantial improvement over running a regex over a string in a quasi-structured log file after the fact (IMHO).

> Divmod experimented with marking log events with interfaces that 
> documented the structure and semantics of the log event carrying them. 
> This didn't get very far, and perhaps had problems of its own, but even 
> it seemed preferable to either of the above options.

What I'd really like to do is to have some kind of log object built up like this:

logger = Logger(module=__name__)

class DebugFoo(logger.message()):
   """wouldn't it be great if such messages were explained in detail"""
   audience=developers; importance=medium; format="foo %(foo)d happened";

def onFoo(someFoo):

and while this isn't hard to implement, it's also not implemented already, but the format= stuff is.  So my suggestion was not intended to say we should stop here, but rather, while we're figuring out better stuff to do, nobody should ever write a 'log.msg("some static " + thing)' again :).


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