Python: truncated logging level names (string formatting) customization

Question

I am using pythons logging module, and I would like to have a simple change to my logging message. Here is what the formatter looks like, and the result:

console_err_format = logging.Formatter(
    str("%(asctime)s - " + "%(levelname)s" +" - %(message)s"),
    "%H:%M:%S")

12:35:33 - INFO - Assessing reads and library type
12:35:33 - DEBUG - Checking reads...
12:35:33 - WARNING - Error while checking reads...

I would like just the first character of the logger level to be shown:

12:35:33 - I - Assessing reads and library type
12:35:33 - D - Checking reads...
12:35:33 - W - Error while checking reads...

Does anyone know how to do this? I have tried the following things, to no avail:

# attempt 1
console_err_format = logging.Formatter(
    str("%(asctime)s - " +"{0}".format("%(levelname)s"[:1]) +" - %(message)s"), "%H:%M:%S")
# attempt 2
console_err_format = logging.Formatter(
    str("%(asctime)s - " +"%(levelname)s"[:1] +" - %(message)s"), "%H:%M:%S")

Any tips would be appreciated! Bonus points if anyone has figured out howto integrate one of the color logging modules!

Answer 1

Use the format specifier for 1-character precision, as in the following example:

>>> import logging
>>> logging.basicConfig(level=logging.DEBUG, format='%(asctime)s %(levelname).1s %(message)s')
>>> logging.debug('Message should be as required')
2017-11-01 00:47:31,409 D Message should be as required
>>> logging.warning('Warning message should be as required')
2017-11-01 00:47:50,702 W Warning message should be as required
>>> 

Note the .1 in front of the s in the %(levelname) specifier, which restricts the output for that value to one (the first) character.

Answer 2

I'm not sure how to do it with a formatter, but you can replace the built in level name strings with your own. For example:

logging.addLevelName(logging.WARNING, 'W')

replaces the string associated with the WARNING level with the single character 'W'. Repeating the above for all levels will have the desired effect.