Dynamically change logging formatter in python?

Question

I am using python logging, at one point of program I need a logging format like this,

"[%(asctime)s] [%(service_id)s] [%(
    levelname)s] [%(hostname)s] [%(host_ip)s] [%(client_agent)s] [%(client_ip)s] [%(filename)20s:%(lineno)d]"

at another point I need a format like this and so on,

 "[%(asctime)s] [%(service_id)s] [%(
    levelname)s] [%(hostname)s] [%(host_ip)s]"

My logging format should dynamically change through out the program. How to achieve this?

You could just call handler.setFormatter(...) everytime you need a new format? — blues
– blues, Commented May 10, 2021 at 12:39

bjornaer · Accepted Answer · 2021-05-11 18:53:09Z

2

you can change the format by calling:

logging.basicConfig(format="%(asctime)s %(service_id)s %(
levelname)s %(hostname)s %(host_ip)s %(message)s")

or

logging.basicConfig(
  format="%(asctime)s {} %(message)s".format(get_your_hostname_somewhere())
)

the above as pointed by blues comment, would work on the initial setup only.

I believe to get hostname(and all the other fancy data) in there like that you will need to implement a logging.Filter or format it into your logged message if they are defined in the context you call your logger.

After a second review I came across this HOWTO which might be helpful as well, a given example would be something along the lines of:

import logging

# create logger
logger = logging.getLogger('simple_example')
logger.setLevel(logging.DEBUG)

# create console handler and set level to debug
ch = logging.StreamHandler()
ch.setLevel(logging.DEBUG)

# create formatter
formatter = logging.Formatter('%(asctime)s %(service_id)s %(
levelname)s %(hostname)s %(host_ip)s %(message)s')

# add formatter to ch
ch.setFormatter(formatter)

# add ch to logger
logger.addHandler(ch)

logger.info("message")

and on the other file get the logger and define a handler once more, but define the Formatter with the new format.

edited May 11, 2021 at 18:53

answered May 10, 2021 at 12:56

bjornaer

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2 Comments

blues Over a year ago

This doesn't work. basicConfig can only be used to setup logging once. Calling it again will not change the format (or anything else)

bjornaer Over a year ago

@blues indeed, thank you for mentioning it. edited response to try and make it more clear, also found more documentation that might provide helpful for this case!

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