[Python-Dev] PEP 461 - Adding % and {} formatting to bytes

[Paul Moore]

On 17 January 2014 15:50, Eric V. Smith <eric at trueblade.com> wrote:
> For #3, hopefully this "additional work" on the 3.x side would just be
> to add, to each class where you already have a custom __format__ used
> for b''.format(), code like:
>
>     def __format_ascii__(self, fmt):
>         return self.__format__(fmt.decode()).encode('ascii')

For me, the big cost would seem to be in the necessary documentation,
explaining the new special method in the language reference,
explaining the 2 different forms of format() in the built in types
docs. And the conceptual overhead of another special method for people
to be aware of. If I implement my own number subclass, do I need to
implement __format_ascii__?

My gut feeling is that we simply don't implement format() for bytes. I
don't see sufficient benefit, if %-formatting is available.

Paul.