Country-specific BBAN checks

[mhemeryck]

Hi all, I have question related to country-specific BBAN checks.

It seems this library does not implement those checks?

Given that I like the developer API and the overall setup of this project, I would be interested to know if and how we could implement such a feature.

In broad terms, I am thinking of a custom exception (invalidBBAN?) when doing the validation of the IBAN.

[mdomke]

Hey @mhemeryck, sorry for the late reply. I think one would have to extend the IBAN.validate()-method, so that it calls a method like IBAN._validate_bban(). In that method one would select the appropriate checksum algorithm based on the country code. If this check fails I would raise an InvalidBBAN-exception. Maybe it is worth thinking about making this additional check optional e.g. by adding a parameter like allow_invalid_bban=True to the IBAN-constructor.

[mhemeryck]

That would actually be really great! Thanks a lot already!

[mdomke]

I added support for country specific BBAN checksums in #50. This currently includes the account code checksum verification for German banks and the BBAN checksum verification for Italian banks. If you wanted to add algorithms for Belgian banks have a look at the abstract base class Algorithm in schwifty.checksum. It has two methods compute and validate which have to be implemented by algorithms that should be added to the "algorithms library". Each algorithm class has a name class-variable which is used for identification. The schwifty.checksum.register-function should be used to add an algorithm to the library by providing the country code (e.g. "BE") as a prefix. In Germany there are over 150 different algorithms from which banks can chose. I adapted the german bank registry file so that each entry maps to the respective algorithm name. I don't know if you would need something similar in your case as well. Have a look at the IBAN._validate_bban_checksum-method to see how the actual algorithm selection is done. You can also have a look at schwifty.checksum.germany as inspiration on how to implement those algorithm classes. If you have any further questions don't hesitate to ask!

[mhemeryck]

Thx a lot for all the work!

I also really like the new API you added there for the BBAN checksum validation.

Fortunately, for the case of Belgium, it's a bit easier than for Germany (we only have 1 algorithm as I understand it).

See #51 for my implementation.

[mdomke]

@mhemeryck thank you very much for your contribution! I created a new release 2021.05.2 which includes your changes.

[mhemeryck]

Thanks a lot!

My contribution was fairly limited since it could readily build on the new API you did create 🙂