Can't chain .opt() calls

[gazpachoking]

Calling opt more than once on a logger instance overrides all options that aren't specified to default, meaning you can't chain .opt() calls together.
For example in the following call, the color codes are ignored.

logger.opt(ansi=True).opt(depth=1).debug('<red>aoeu</>')

This doesn't make a lot of sense when done directly like this, but if you are using the recipe for adding custom loglevel methods, it calls .opt() to set the depth. The consequence of this is that you can no longer use .opt() directly from you code, since it will always be overridden by the depth call, including all of the options other than depth.

[Delgan]

Huh, this is a serious design issue indeed. Thanks for the report and the pull request.

I'm not a big fan of sentinel values, as it makes the signature of the function less readable. I wonder if there is any other possible workaround... If not, I will probably merge your fix. 👍

[gazpachoking]

Could switch to **kwargs instead of having a sentinel value... but that makes the signature even worse. Not sure a better way. At least the signature in the pyi file is still nice with type hints.

[Delgan]

I don't think there's much point in chaining opt() calls, apart from the problem with custom levels you've raised. So, what do you think of replacing the documented recipe with:

from functools import partialmethod

logger.__class__.foobar = partialmethod(logger.__class__.log, "foobar")

I was delightfully surprised to find out that it worked just fine! I guess the Python interpreter somehow optimize partialmethod() so it does not add another frame to the stack, thus avoiding the need for opt(depth=1). Then the foobar() logging method can be combined with any opt() attribute without problem.

[gazpachoking]

I think that recipe change sounds like a good plan regardless of whether opt gets changed.
I sorta like the idea of it working as expected when chained, but it's much less important with that updated recipe. The only other instance I can think of is if someone perhaps wanted to do something like turn on colors by default when logging in only one of their modules. e.g.

from loguru import logger

logger = logger.opt(ansi=True)


try:
    somethingdangerous()
except:
    logger.opt(exception=True).debug('Everything <blue>went</> wrong')

[Delgan]

It seems possible to achieve the desired behavior using the same principle:

from functools import partial

logger = logger.opt(ansi=True)
logger.opt = partial(logger.opt, ansi=True)

Of course, this is not very intuitive, so this recipe needs to be properly documented. Nevertheless, I prefer this workaround. None of the solutions are perfect, so it's a matter of perspective, and I think it's more important to have a "clean" signature rather than allowing opt() chain calls (actually, see 2b8e6f9).

[gazpachoking]

Sounds good, I'll defer to you on this one. Might also be worth a mention in the .opt docs that the last call is the only one that takes effect.

[Delgan]

I updated the recipe for custom level, created a new entry about opt(ansi=True) and added a note in the opt() documentation. Thanks again for the report. 😉

[gazpachoking]

Awesome, looks good. Thanks!

[mifluder]

Do You have any way of working with logger.__class__.foobar = partialmethod(logger.__class__.log, "foobar") and mypy? Obviously mypy can't see that loguru.logger has attribute "foobar" and I didn't find any WA for this.

[Delgan]

@michalplat I think your problem relates to this mypy issue: python/mypy#5363

There is even a comment mentioning the exact same problem but using the standard logging library. Unfortunately, there does not seem to be an accepted solution. 😬

[mifluder]

Thanks for Your input 😄 I think I'll just use pure .log( in that situation. Maybe this is possible area of interests of @kornicameister and loguru-mypy plugin? I am not aware what are plugins used for but maybe for this 😁 If I come up with neat solution I'll update here but I don't have much hope for it😉

[kornicameister]

I don't think I will be able to make any changes. Frankly I am quite busy nowadays. If you feel like you're up too, give it a shot.