[Python-Dev] Re: PEP 282 comments (original) (raw)

Trent Mick trentm@ActiveState.com
Thu, 21 Mar 2002 00:46:05 -0800

[Jeremy Hylton wrote]

It seems quite plausible to decide to log an exception and then get another trivial exception raised and caught on the way to the logger. You would still want to log the original exception, so passing it explicitly is helpful sometimes.

Yes, I suppose so.

If I would implement debug() and other helper methods, I'd still like to see it as a keyword argument. I assume the various methods would be connected something like this:

class Logger: def log(self, msg, level, exc=None): "Log msg at level w/ optional traceback for exc." def debug(self, msg, exc=None): self.log(msg, DEBUGLEVEL, exc) def exception(self, msg, exc=None): if exc is None: exc = sys.excinfo() self.log(msg, ERRORLEVEL, exc) This doesn't seem complicated or particularly slow.

Yup, I agree. Except it'll look like this:

class Logger: def log(self, level, msg, *args, **kwargs): "Log msg at level w/ optional traceback for 'exc' keyword arg." if level < self.getEffectiveLevel(): return # construct LogRecord # pass LogRecord onto appropriate Handlers

def debug(self, msg, *args, **kwargs):
    self.log(DEBUG, msg, *args, **kwargs)

def exception(self, msg, *args, **kwargs):
    if not kwargs.has_key("exc")
        kwargs["exc"] = sys.exc_info()
    self.log(ERROR, msg, *args, **kwargs)

Jeremy, The methods use 'msg, *args' instead of just 'msg' to avoid string interpolation if the message will not be logged. I think that that is still important to keep, albeit it making the 'exc' keyword argument less explicit.

Vinay, Here is why I really like this idea now. As per usual, any log message call has the 'msg, *args' arguments. But, in addition, arbitrary objects can be passed in as keyword arguments. These objects get slapped into the LogRecord's dict and any subsequent Handler and/or Formatter can work with those objects. For example, if I want to log some arbitrarily complex object I can just add it to the log record. On the handling end, I could have a Formatter that knows how to deal with that object. For formatters that don't recognize certain objects, a reasonable default like using the pprint module could be used.

Granted this isn't as generic as log4j's ObjectRenderer system but it allows the system to grow into that cleanly.

Pros:

Cons:

Trent

-- Trent Mick TrentM@ActiveState.com