Python: can I modify the log contents before logging into a file?

Question

Is there a way to mask the 'SECRET' information in the log with 'xxxxxxx' without changing the last line of code in below.

import logging

logger = logging.getLogger(__name__)
logger.setLevel(logging.DEBUG)
formatter = logging.Formatter('%(asctime)s:%(name)s:%(message)s')
file_handler = logging.FileHandler('sample.log')
file_handler.setFormatter(formatter)
logger.addHandler(file_handler)

logger.info("Information contains SECRET stuff.")

If I run above code, I will get below log content: 2019-08-21 09:47:12,845:main:Information contains SECRET stuff.

Without changing the last line of code: logger.info("Information contains SECRET stuff"), is there a way to generate expected log as below: 2019-08-21 09:47:12,845:main:Information contains xxxxxxxx stuff.

Answer 1

You could inherit from the 'logging.Logger' class and provide your own 'info' method. Note the addition of the 'setLoggerClass' call to switch to the custom class.

import logging

class secretLogger(logging.Logger):

    def __init__(self,name,level=logging.NOTSET):
        super(secretLogger,self).__init__(name,level)

    def info(self,msg,*args,**kwargs):
        secretMsg = msg.replace('SECRET','xxxxxxxx')
        super(secretLogger,self).info(secretMsg,*args,**kwargs)

logging.setLoggerClass(secretLogger)
logger = logging.getLogger(__name__)
logger.setLevel(logging.DEBUG)
formatter = logging.Formatter('%(asctime)s:%(name)s:%(message)s')
file_handler = logging.FileHandler('sample.log')
file_handler.setFormatter(formatter)
logger.addHandler(file_handler)

logger.info("Information contains SECRET stuff.")