🔒 aligning a logging format string field with ":" included | Python | Page 1

coral solstice Mar 25, 2026, 3:14 PM

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I have a logger format string like this

iso_8601 = '%Y-%m-%dT%H:%M:%S'
fmt = "\033[34m{levelname}\033[0m:  {asctime}   {name} - {message} ({filename}:{lineno})"
formatter = logging.Formatter(fmt, iso_8601, style='{')

I want to align the level name together with the : such that the whole thing is 10 characters wide like

INFO:    ...
WARNING: ...
DEBUG:   ...

How could I do it? I know that I can do format on the level name itself, but I am not sure how with the : included

dusky obsidianBOT Mar 25, 2026, 3:14 PM

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coral solstice I have a logger format string like this ```py iso_8601 = '%Y-%m-%dT%H:%M:%S' fmt...

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@coral solstice

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thorny minnow Mar 25, 2026, 3:15 PM

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Are you allowed to add a library or no?

coral solstice Mar 25, 2026, 3:16 PM

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preferably not 🙂

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but I would still like to hear it

thorny minnow Mar 25, 2026, 3:21 PM

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https://docs.python.org/3/howto/logging-cookbook.html#how-to-uniformly-handle-newlines-in-logging-output

Standby, I'm having to figure this out myself

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So what does your code currently output do you have an example?

coral solstice Mar 25, 2026, 3:25 PM

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INFO: 2026-03-25T15:22:43 api.main - App is started! (main.py:31)

thorny minnow Mar 25, 2026, 3:25 PM

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okay now I see your problem thanks

coral solstice Mar 25, 2026, 3:26 PM

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I would want it to be like

INFO:     2026-03-25T15:22:43   api.main - App is started! (main.py:31)
DEBUG:    2026-03-25T15:22:43   api.main - App is started! (main.py:31)

thorny minnow Mar 25, 2026, 3:27 PM

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"\033[34m{levelname+":":<10}\033[0m:  {asctime}   {name} - {message} ({filename}:{lineno})"

I have no idea if that will work

topaz ferry Mar 25, 2026, 3:28 PM

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It's easy to do without the colon... But the colon makes it tricky

coral solstice Mar 25, 2026, 3:28 PM

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I know that's why I asked xd

topaz ferry Mar 25, 2026, 3:28 PM

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thorny minnow ``` "\033[34m{levelname+":":<10}\033[0m: {asctime} {name} - {message} ({filen...

It won't, try the short version (only first part) with .format(levelname="whatever")

thorny minnow Mar 25, 2026, 3:29 PM

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oh for some reason i thought it was an f string lol brain fart

topaz ferry Mar 25, 2026, 3:29 PM

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>>> "{a+':':12}".format(a="info")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: "a+'"

It's easy to just test such stuff in repl before suggesting

coral solstice Mar 25, 2026, 3:29 PM

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aligning a logging format string with ":" included

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aligning a logging format string field with ":" included

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I saw that the logs are aligned like that in fastapi so I want to do it myself too

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ducky_concerned

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https://github.com/Kludex/uvicorn/blob/main/uvicorn/logging.py#L58
they are just hardcoding the values lol

GitHub

uvicorn/uvicorn/logging.py at main · Kludex/uvicorn

An ASGI web server, for Python. 🦄. Contribute to Kludex/uvicorn development by creating an account on GitHub.

split kayak Mar 25, 2026, 3:36 PM

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Hey,

Just use a custom logging.Formatter subclass that overrides format() to inject the padded levelname: before the ANSI codes get in the way

coral solstice Mar 25, 2026, 3:37 PM

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I guess so

thorny minnow Mar 25, 2026, 3:44 PM

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FINALLY

logging.addLevelName(logging.ERROR, "ERROR:")
fmt = "\033[34m{levelname:<10}\033[0m  {asctime}   {name} - {message} ({filename}:{lineno})"

ERROR: 2026-03-25T15:44:22 test_logger - Error message: Another standard level. (main.py:27)

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thanks for posting this. I definitely needed to sharpen my formatting skills

neon nebula Mar 25, 2026, 3:48 PM

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as vincent suggested this works

import logging

iso_8601 = '%Y-%m-%dT%H:%M:%S'

fmt = "\033[34m{levelname:<9}\033[0m: {asctime}   {name} - {message} ({filename}:{lineno})"

logging.basicConfig(
    level=logging.DEBUG,
    format=fmt,
    datefmt=iso_8601,
    style='{'
)

logger = logging.getLogger("api.main")

logger.debug("Debug message")
logger.info("App is started!")
logger.warning("Something might be wrong")
logger.error("Something failed")
logger.critical("Critical issue!")

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expected output

thorny minnow Mar 25, 2026, 3:49 PM

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That's not what he's looking for

neon nebula Mar 25, 2026, 3:50 PM

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neon nebula expected output

this makes it, 10 char wide

thorny minnow Mar 25, 2026, 3:51 PM

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import logging

iso_8601 = '%Y-%m-%dT%H:%M:%S'

logging.addLevelName(logging.ERROR, "ERROR:")
logging.addLevelName(logging.WARNING, "WARNING:")
logging.addLevelName(logging.DEBUG, "DEBUG:")
logging.addLevelName(logging.INFO, "INFO:")
logging.addLevelName(logging.CRITICAL, "CRITICAL:")
fmt = "\033[34m{levelname:<10}\033[0m  {asctime}   {name} - {message} ({filename}:{lineno})"

logging.basicConfig(
    level=logging.DEBUG,
    format=fmt,
    datefmt=iso_8601,
    style='{'
)

logger = logging.getLogger("api.main")

logger.debug("Debug message")
logger.info("App is started!")
logger.warning("Something might be wrong")
logger.error("Something failed")
logger.critical("Critical issue!")

DEBUG:      2026-03-25T15:51:00   api.main - Debug message (main.py:21)
INFO:       2026-03-25T15:51:00   api.main - App is started! (main.py:22)
WARNING:    2026-03-25T15:51:00   api.main - Something might be wrong (main.py:23)
ERROR:      2026-03-25T15:51:00   api.main - Something failed (main.py:24)
CRITICAL:   2026-03-25T15:51:00   api.main - Critical issue! (main.py:25)

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@coral solstice

coral solstice Mar 25, 2026, 3:53 PM

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you can edit the level names? wow

dusky obsidianBOT Mar 25, 2026, 4:53 PM

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#🔒 aligning a logging format string field with ":" included