Use str.format()-style logging formatting instead of '%'

[Chris Lamb]

We currently use the %(foo)s style in Django and in docs. This "smells" quite Python 2.x when there is a str.format variety that uses, eg. {foo}.

[Chris Lamb]

PR ​https://github.com/django/django/pull/9359

[Tim Graham]

I'm not sure why you say "Python 3-esque str.format" in the description. str.format() was added in Python 2.6. I see that logging support for that style (by using style='{') was added in Python 3.2.

I'm not opposed to the change, as it seems like a slight readability enhancement, although generally I think there's a consensus against using mandating str.format() usage everwhere in Django and prohibiting the %s syntax. I think there was a ticket but I can't find it at the moment.

My only concern with the proposal is whether it could break backwards compatibility. I see an update to ServerFormatter.uses_server_time() was required. I'm not sure if it's likely that user code may make similar assumptions about the format string.

[Chris Lamb]

Replying to Tim Graham:

I'm not sure why you say "Python 3-esque str.format" in the description. str.format() was added in Python 2.6.

I should have used a better suffix than "esque" — it's more that Python 3 code does tend to *prefer* str.format over %-style interpolation simply as a correlation with it being more modern/newer in general. ie. if it's "new enough" for Python 3, it's probably going to be using newer/nicer features. It's therefore somewhat surprising to see the reverse, hence this proposed change.

there's a consensus against using mandating str.format() usage everwhere in Django and prohibiting the %s syntax.

As it happens, I would be against such a total mandate and a widespread change *within* Django, but this is more of a user-exposed thing so a different, separate argument IMHO.

[Tim Graham <timograham@…>]

In 3af305e8:

Fixed #28810 -- Replaced '%' style logging formatting with str.format() style.