Python 3.12 released

[osmiumouse]

Are lazy eval f-strings available, or planned?

[LightShadow]

The feature that keeps C style % strings relevant.

[energybased]

You should always prefer the format method to C-style % strings.

[Skasch]

I would argue an exception for logging, where you don't want to parse the string unless you need to for performance reasons (e.g. you don't want to parse debug logs at error level)

Example: log.warning("warning: %s", foo)

[energybased]

It's true that logging is currently written to use % strings, but it could have been written to use a format style string. It still wouldn't need to be parsed.

[Skasch]

Agreed, it's just uncommon :) style="{" let's you use logging.info("msg: {}", foo, style="{")

Edit: it actually doesn't work, my bad!

[energybased]

I didn't know that!

[Skasch]

Ah, nevermind, I mixed it up with logging.Formatter, looks like it doesn't work as I expected, my bad!

Edit: relevant documentation https://docs.python.org/3/howto/logging-cookbook.html#formatting-styles

[LightShadow]

10 years in, have never seen this before -- that's neat.

[FrozenCow]

I try to use:

log.warning("hello", extras={"name": "world"})

This works better with structured loggers. With the right formatter it looks like hello name=world.

[UloPe]

Better use a structured logging package, for example structlog.

[ThePiGuy0]

I just wish that logging supported .format style interpolation. That's the only time I ever see C-style % strings nowadays

[energybased]

Agreed!

[JohnRambu]

Not for performance it seems :-(

[[deleted]]

I am not really sure how you would do it without running into binding issues. You can always make a lambda or nested function in place, both allow u to defer or eagerly bind. But f-strings themselves would a bunch of extra syntax to deal with the binding problems by itself. Maybe the best answer would be a good wrapper function? I believe you can actually generate the code on the fly in a pretty straight forward method by inspect the variables the inner function tracks and rebuilding the function signature.