mark lazy mode is deprecated and add LazyValue for lazy format value

[trim21]

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[trim21]

ci failed at codecov, not test/lint

[Delgan]

Hi @trim21, thanks for opening a PR. I understand it refers to #1207.

I've been thinking about this lately, and to be honest I'm not very keen on the idea adding a new LazyValue class just to optimize lazy evaluations of message formatting. So far, the logger has been the only publicly importable component from loguru. That would be a significant change of this idiom for what seems to be a relatively small inconvenience.

I would welcome a new API for lazy evaluated arguments if it also address #782. However, this is not necessarily easy.

Another thing to consider is PEP 750. It's still draft and there's no guarantee that it will be accepted, but it could be interesting for our use case, without requiring a new API.

[trim21]

maybe we can add a api logger.lazy(fn, *args, **kwargs)?

I don't think PEP 750 will help #782 or this, even with pep750 accepted, value in template str is still calculcated before logger function is called.

[trim21]

also we have only sync api, I don't know there is a method to handle #782

[Delgan]

value in template str is still calculcated before logger function is called.

Indeed, but it's possible to pass a lambda: Approaches to Lazy Evaluation

We could imagine than when a template string is used, then Loguru will convert callable arguments, but only if the log level requires it. This would make the opt(lazy=true) argument obsolete, while making it straightforward to combine with non-lazy arguments.

This PEP is actively discussed here.

maybe we can add a api logger.lazy(fn, *args, **kwargs)?

I would prefer such API, yes. But still, that's a new method that increases the complexity of Loguru's API, for a marginal gain in my opinion.

also we have only sync api, I don't know there is a method to handle #782

Yes, unfortunately I don't know how to integrate it either.

[trim21]

We could imagine than when a template string is used, then Loguru will convert callable arguments, but only if the log level requires it.

personal I think this is confusing and dangerous behaviour to call callable in arguments unless explicit specified with lazy or something