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's something real simple that works:

debug_logger: logging.Logger = logging.getLogger("app.debug")

def mydebuglog(msg: str, *args, **kwargs):
    if debug_logger.isEnabledFor(logging.DEBUG):
        debug_logger.debug(msg.format(*args, **kwargs))

Then:

mydebuglog("hello {} {val}", "Python", val="World")

Answer 2

Similar solution to pR0Ps' , wrapping getMessage in LogRecord by wrapping makeRecord (instead of handle in their answer) in instances of Logger that should be new-formatting-enabled:

def getLogger(name):
    log = logging.getLogger(name)
    def Logger_makeRecordWrapper(name, level, fn, lno, msg, args, exc_info, func=None, extra=None, sinfo=None):
        self = log
        record = logging.Logger.makeRecord(self, name, level, fn, lno, msg, args, exc_info, func, sinfo)
        def LogRecord_getMessageNewStyleFormatting():
            self = record
            msg = str(self.msg)
            if self.args:
                msg = msg.format(*self.args)
            return msg
        record.getMessage = LogRecord_getMessageNewStyleFormatting
        return record
    log.makeRecord = Logger_makeRecordWrapper
    return log

I tested this with Python 3.5.3.

Answer 3

I created a custom Formatter, called ColorFormatter that handles the problem like this:

class ColorFormatter(logging.Formatter):

    def format(self, record):
        # previous stuff, copy from logging.py…

        try:  # Allow {} style
            message = record.getMessage()  # printf
        except TypeError:
            message = record.msg.format(*record.args)

        # later stuff…

This keeps it compatible with various libraries. The drawback is that it is probably not performant due to potentially attempting format of the string twice.