[Python-Dev] RFC: PEP 460: Add bytes % args and bytes.format(args) to Python 3.5

[Stephen J. Turnbull]

Antoine Pitrou writes:

 > However, interpolating a bytes object isn't out of place, and it is
 > what a minimal "formatting" primitive could do.

Something like this?

    # VERY incomplete pseudo-code
    class str:

        # new method
        # fmtstring has syntax of .format method's spec, maybe adding a 'B'
        # for "insert Blob of bytes" spec
        def format_for_wire(fmtstring, args, encoding='utf-8', errors='strict'):

            result = b''

            # gotta go to a meeting, exercise for reader :-(
            parts = zip_specs_and_args(fmtstring, args)

            for spec, arg in parts:
                if spec == 'B' and isinstance(arg, bytes):
                    result += arg
                else:
                    partial = format(spec, arg)
                    result += partial.encode(encoding=encoding, errors=errors)

            return result

Maybe format_to_bytes is a more accurate name.

I have no idea how to do this for %-formatting though. :-(

And I have the sneaking suspicion that it *can't* be this easy. :-(

Can it? :-)