Confusing error text

[anton-kazlouski]

I'm not English native, but the error message seems to have a logical error:
This field may not be null -- means that a field might be null and might not be null (negative probability). But the translation means that the field is required and cannot be null.

django-rest-framework/rest_framework/locale/ru_RU/LC_MESSAGES/django.po

Line 160 in 3578683

msgid "This field may not be null."

I've checked with Django sources and found this:
This field cannot be null which seems to me more accurate.

I want to clarify it's an actual mistake. If yes, I'll create a PR to fix this issue.

[tomchristie]

Any of "cannot", "must not", "may not" would be okay here.
There's subtle differences in meaning, but they're mostly close enough to the same thing in this context.

Personally I probably marginally prefer "must not" or "may not", which implies "is not permitted", rather than cannot, which implies "is not possible".

I doubt we'll change it since it'd end up marking all the translations as needing re-translating (although they probably wouldn't actually), but I can see that determining exactly which phrasing would be most suitable for an international audience is a gray area.

[n2ygk]

Happily someone else already figured out the English ambiguity for us: https://tools.ietf.org/html/bcp14

[anton-kazlouski]

Originally, this question araised when I was reviwened a PR to the other projects. And found the following phrase:
This field is required, may not be null or blank

A developer said that he used DRF sources as a reference. Seems like, This field is required creates this contradiction.

[anton-kazlouski]

@tomchristie I won't push the idea of changing the entire project just to be as precise as possible. But could you, please, clarify this one moment, just to satisfy my sense of curiosity:
Personally I probably marginally prefer "must not" or "may not", which implies "is not permitted"

According to the link provided by @n2ygk and Cambridge dictionary may is not used in prohibition function.

[tomchristie]

Sure.

I can see some sense in technical writing prefering the more authorative "must not", because in a way "may" and "may not" do not exactly mean the logical inverse of each other.

"you may do this" means this "this is allowed". (But it's optional, you don't have to.)
"you may not do this" means "this is not allowed". (It doesn't mean, "this is optionally not allowed", which would be a nonsense.)

[anton-kazlouski]

I see now. Thanks!