How to right align level field in Python logging.Formatter

Question

I'm currently trying to right align the logging level field in my Python logger so that output such as:

[2011-10-14 13:47:51] [DEBUG] --- starting... (smtphandlers.py:96) [2011-10-14 13:47:51] [INFO] --- first things first... (smtphandlers.py:97) [2011-10-14 13:47:51] [WARNING] --- about to end... (smtphandlers.py:98) [2011-10-14 13:47:51] [DEBUG] --- ending (smtphandlers.py:99)

instead looks like:

[2011-10-14 13:47:51] [ DEBUG] --- starting... (smtphandlers.py:96) [2011-10-14 13:47:51] [ INFO] --- first things first... (smtphandlers.py:97) [2011-10-14 13:47:51] [ WARNING] --- about to end... (smtphandlers.py:98) [2011-10-14 13:47:51] [ DEBUG] --- ending (smtphandlers.py:99)

The format line for the first block is:

logging.Formatter("[%(asctime)s] [%(levelname)s] --- %(message)s (%(filename)s:%(lineno)s)", "%Y-%m-%d %H:%M:%S")

If I know the max level length is 8 (eg: CRITICAL), then I'll right align to 8 spaces. I'm trying to figure out how to achieve this. The following fails because "%(levelname)s" is more than 8 characters (the substitution doesn't happen until later). If I use something like "{0:>20}".format"%(levelname)s", then it works, but that is more padding than I need or want.

logging.Formatter("[%(asctime)s] [" + "{0:>8}".format"%(levelname)s" + "] --- %(message)s (%(filename)s:%(lineno)s)", "%Y-%m-%d %H:%M:%S")

Short of subclassing Formatter, anyone have a way to achieve this?

The %(...)s is called printf-style String Formatting. We're able to adjust the string width by setting the "minimum field width" or left align the content by using a "-" (dash or hyphen) "conversion flags". — li ki
– li ki, Commented Jul 16, 2022 at 2:48

vvvvv · Accepted Answer · 2023-01-09 16:32:29Z

125

Like this:

logging.Formatter("[%(asctime)s] [%(levelname)8s] --- %(message)s (%(filename)s:%(lineno)s)", "%Y-%m-%d %H:%M:%S")

PS: If you would like INFO to be left aligned, you can use [%(levelname)-8s] instead.

edited Jan 9, 2023 at 16:32

vvvvv

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answered Oct 14, 2011 at 18:31

retracile

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2 Comments

Joe Over a year ago

@AlexL What about center aligned?

wjh18 Over a year ago

@JoeVictor Late to the party but this can be done by setting the style parameter for the Formatter object to { and doing something like [{levelname:^8s}].

Clay Records · Accepted Answer · 2019-10-01 16:00:29Z

Try with this format line :

logging.Formatter("[%(asctime)s] [%(levelname)8s] --- %(message)s (%(filename)s:%(lineno)s)", "%Y-%m-%d %H:%M:%S")

python logger formatter use the standard python string formatting rules

%8(levelname)s won't work, it needs to be %(levelname)8s.

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