On Sat, May 28, 2011 at 12:43 PM, Eric Smith <eric@trueblade.com> wrote:
And Python 3.x has the exact same implementation, although it's only included for unicode strings. It would not be difficult to add .format() for bytes.
There have been various discussions over the years of how to actually do that. I think the most recent one was to add an __bformat__ method.
Well, that's actually great idea I think. format method on bytes could produce some data which is not an ascii, and eventually became struct.pack on steroids. The struct.pack has plenty of problems: * unable to use named fields, which is usefull to describe big structures * all fields are fixed-length, which is unfortunate for today's trend of variable length integers * can't specify separators between fields I also use str(intvalue).encode('ascii') idiom a lot. So probably I'd suggest to have something like __bformat__ with format values somewhat similar to ones struct.pack has along with str-like ones for integers. Also it might be useful to have `!len` conversion for bytes fields, for easier encoding of length-prefixed strings. To show an example, here is how two-chunk png file can be encoded: (b"\x89PNG\r\n\x1A\n" b"{s1!len:>L}IHDR{s1}{crc1:>L}" b"{s2!len:>L}IDAT{s2}{crc2:>L}\0\0\0\0IEND".format( s1=section1, crc1=crc(section1), s2=section2, crc2=crc(section2))) -- Paul