Reduce amount of redundant code in django.contrib.localflavor

[Piotr Lewandowski <django@…>]

There is a plenty of somehow redundant code in django.contrib.localflavor which leads to potentially more bugs and what is quite inconvenient -- many translation strings.

I would like to propose the patch that handles all fields with a checksum verification.

Pros:

• a lot fewer translation strings, which is more consistent and means less work when translating Django to 50 languages,
• DRY compatible (and all benefits that it implies).

Cons:

• backwards incompatible,
• new code may contain bugs (although all tests were OK).

I volunteer for further modifications of django.contrib.localflavor code to use NumberWithChecksumField if this patch is accepted.

[Piotr Lewandowski <django@…>]

I forgot to mention that this patch also fixes a bug in PLNationalBusinessRegisterField. This field should accept also 14-digit numbers (see ​http://www.stat.gov.pl/bip/389_117_ENG_HTML.htm for reference).

[Malcolm Tredinnick]

It should be possible to do this in a backwards-compatible fashion by declaring specific classes in each localflavor that are specific cases of a parameterised parent class. The intention here is good, since there is some quite apparent duplication, but right now isn't the time to be shuffling this code around. Let's table until after 1.0.

[(none)]

Milestone post-1.0 deleted

[Julien Phalip]

Patch needs improvement as per Malcolm's comment.

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Localflavor has just been split in distinct repositories, making this refactoring significantly harder and less likely to happen.

Besides, I think that descriptive error messages are important for usability, even if they come at the cost of more translation strings.