DurationField's overflow error message fails to translate

[Jannis Leidel]

In ​https://github.com/django/django/commit/55b5393bd235aa6c55ea9a7da6f0e8b75b204084 a new ValidationError message was added that isn't using the common pattern of using string substitution variables but instead a format string.

I noticed this while updating the German translation for 2.1 and found Transifex to not display the variables correctly which could prevent translators to correctly set the variables in the translated string.

In my experience translators can mistake "{variables}" in text as something to translate as well, which effectively can lead to either KeyError (because the expected format variable weren't found) or empty fill-ins.

Either way, this is a possible breaking change.

[Markus Holtermann]

PR: ​https://github.com/django/django/pull/10255/files

[Carlton Gibson]

Patch seems fine.

(Slight niggle: Isn't %-style string formatting discouraged now?[1] Does this kind of consideration block moving away from it, assuming that's desirable?)

[1]: "This method of string formatting is the new standard in Python 3, and should be preferred to the % formatting described in String Formatting Operations in new code." ​https://docs.python.org/2/library/stdtypes.html#str.format — though it doesn't say this at ​https://docs.python.org/3/library/stdtypes.html#str.format...

[Markus Holtermann]

I don't think the .format() option works with gettext though, does it?

[Claude Paroz]

Replying to Markus Holtermann:

I don't think the .format() option works with gettext though, does it?

It does. I don't recall the exact gettext version the support was added to, but it works.

Sorry Jannis, but I don't think this is a bug. Even if the older %()s syntax is not deprecated, I see more and more Python code using the 'string'.format() syntax. Translators have to get used to the new syntax anyway. Moreover, if the content is mistakenly translated, msgfmt -c will notice it as an error (the string is marked #, python-brace-format in the po files) and we will not accept the file in Django. The fact that Transifex accepts the wrong translation is a bug in Transifex.

[Claude Paroz]

In fact, regardless of the placeholder style, there might be a bug about the translation happening partially at import time instead of validation time. Anyway, a test is required.

[Tim Graham]

I confirmed Claude's suspicion and updated the ​PR.

[Tim Graham <timograham@…>]

In 730173d1:

Fixed #29623 -- Fixed translation failure of DurationField's "overflow" error message.

[Tim Graham <timograham@…>]

In e3be4e9:

[2.1.x] Fixed #29623 -- Fixed translation failure of DurationField's "overflow" error message.

Backport of 730173d1c5cf210d8e3bd951fa49f64b9bc561ca from master