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

Antoine Pitrou solipsis at pitrou.net
Sat Jan 11 02:12:58 CET 2014

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.

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