Question

I have a logging setup in python application that logs into file and MongoDB. The setup looks like this:

[logger_root]
handlers=myHandler,mongoHandler
level=DEBUG
qualname=myapp

[handler_myHandler]
class=handlers.RotatingFileHandler
level=DEBUG
formatter=myFormatter
args=('myapp.log', 'a',20000000,10)

[handler_mongoHandler]
class=myapp.MongoLogger.MongoLogger
level=INFO
args=('log',)

[formatter_myFormatter]
format=%(asctime)s - %(name)s - %(levelname)s - %(message)s

And the MongoLogger has emit() function like this:

def emit(self, record):
    logdata = record.__dict__
    try:
        if(self.data == None):
            self.initDb()
        self.logtable.insert(logdata)
    except:
       self.handleError(record)

The logging is done like this then:

 logger.info("Processing account %s..." % account)

It works reasonably well, but now I have an additional requirement. I want it to have some context – i.e., to be able to define custom value – say, account name – so every log done inside the account processing would have the account name as part of the record passed to emit above and also available for the formatter in myFormatter string.

Is it possible to do this with logging module? Is there maybe another, better way to do the same?

Answer 1

You can define a function inside the account processing code, after you get the account name, like this:

# account_name should already be defined
log = lambda msg: logger.info(msg, extra={'account': account_name})

###

log('Processing account...')

Note the extra keyword argument. It is used to add additional context to log records—in this case, the account name.

You can use context passed via extra in the formatter:

format = '%(asctime)s - %(name)s - %(levelname)s - %(message)s - %(account)s'

Note that if you set up formatter like this and forget to pass account, you’ll get a string formatting exception.

• More information on extra keyword argument