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

[Antoine Pitrou]

On Fri, 10 Jan 2014 16:23:53 -0800
Ethan Furman <ethan at stoneleaf.us> wrote:
> On 01/08/2014 02:42 PM, Antoine Pitrou wrote:
> >
> > With Victor's consent, I overhauled PEP 460 and made the feature set
> > more restricted and consistent with the bytes/str separation.
> 
>  From the PEP:
> =============
> > Python 3 generally mandates that text be stored and manipulated as
> >  unicode (i.e. str objects, not bytes). In some cases, though, it
> >  makes sense to manipulate bytes objects directly. Typical usage is
> >  binary network protocols, where you can want to interpolate and
> >  assemble several bytes object (some of them literals, some of them
> >  compute) to produce complete protocol messages. For example,
> >  protocols such as HTTP or SIP have headers with ASCII names and
> >  opaque "textual" values using a varying and/or sometimes ill-defined
> >  encoding. Moreover, those headers can be followed by a binary
> >  body... which can be chunked and decorated with ASCII headers and
> >  trailers!
> 
> As it stands now, the PEP talks about ASCII, about how it makes sense
> sometimes to work directly with bytes objects, and 
> then refuses to allow % to embed ASCII text in the byte stream.

Indeed I refuse for %-formatting to allow the mixing of bytes and str
objects, in the same way that it is forbidden to concatenate "a" and
b"b" together, or to write b"".join(["abc"]).

Python 3 was made *precisely* because the implicit conversion between
ASCII unicode and bytes is deemed harmful. It's completely
counter-productive and misleading for our users to start mudding the
message by introducing exceptions to that rule.

Regards

Antoine.