Logging variable data with new format string

Question

I use logging facility for python 2.7.3. Documentation for this Python version say:

the logging package pre-dates newer formatting options such as str

Answer 1

Here is another option that does not have the keyword problems mentioned in Dunes' answer. It can only handle positional ({0}) arguments and not keyword ({foo}) arguments. It also does not require two calls to format (using the underscore). It does have the ick-factor of subclassing str:

class BraceString(str):
    def __mod__(self, other):
        return self.format(*other)
    def __str__(self):
        return self


class StyleAdapter(logging.LoggerAdapter):

    def __init__(self, logger, extra=None):
        super(StyleAdapter, self).__init__(logger, extra)

    def process(self, msg, kwargs):
        if kwargs.pop('style', "%") == "{":  # optional
            msg = BraceString(msg)
        return msg, kwargs

You use it like this:

logger = StyleAdapter(logging.getLogger(__name__))
logger.info("knights:{0}", "ni", style="{")
logger.info("knights:{}", "shrubbery", style="{")

Of course, you can remove the check noted with # optional to force all messages through the adapter to use new-style formatting.

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Note for anyone reading this answer years later: Starting with Python 3.2, you can use the style parameter with Formatter objects:

Logging (as of 3.2) provides improved support for these two additional formatting styles. The Formatter class been enhanced to take an additional, optional keyword parameter named style. This defaults to '%', but other possible values are '{' and '$', which correspond to the other two formatting styles. Backwards compatibility is maintained by default (as you would expect), but by explicitly specifying a style parameter, you get the ability to specify format strings which work with str.format() or string.Template.

The docs provide the example logging.Formatter('{asctime} {name} {levelname:8s} {message}', style='{')

Note that in this case you still can't call the logger with the new format. I.e., the following still won't work:

logger.info("knights:{say}", say="ni")  # Doesn't work!
logger.info("knights:{0}", "ni")  # Doesn't work either