[Python-Dev] PEP 461: Adding % formatting to bytes and bytearray -- Final, Take 3

[Glenn Linderman]

On 3/27/2014 11:59 AM, Guido van Rossum wrote:
> On Thu, Mar 27, 2014 at 11:52 AM, Daniel Holth <dholth at gmail.com 
> <mailto:dholth at gmail.com>> wrote:
>
>     I feel not including %s is nuts. Should I write .replace('%b', '%s')?
>
>
> I assume you meant .replace('%s', '%b') (unless you're converting 
> Python 3 code to Python 2, which would mean you really are nuts :-).
>
> But that's not going to help for the majority of code using %s -- as I 
> am trying to argue, %s doesn't mean "expect the argument to be a str" 
> and neither is that how it's commonly used (although it's *possible* 
> that that is how *you* use it exclusively -- that doesn't make you 
> nuts, just more strict than most people).

That _is_ how it is commonly used in Py2 when dealing with binary data 
in mixed ASCII/binary protocols, is what I've been hearing in this 
discussion, and what small use I've made of Py2 when some unported 
module forced me to use it (I started Python about the time Py3 was 
released)... the expected argument is a (Py2) str containing binary data 
(would be bytes in Py3).

While there are many other reasons to use %s in other coding situations, 
this is the only way to do bytes interpolations using %. And there is no 
%b in Py2, so for Py2/3 compatibility, %s needs to do bytes 
interpolations in Py3. And if it does, there is no need for %b in Py3 %, 
because they would be identical and redundant.

>     All I desperately need are APIs that provide enough unicode / str type
>     safety that I get an exception when mixing them accidentally... in my
>     own code, dynamic typing is usually a bug. As has been endlessly
>     discussed, %s for bytes is a bit like exposing sprintf()...
>
>
> I don't understand that last claim (I can't figure out whether in this 
> context is exposing sprintf() is considered good or bad). But apart 
> from that, can you give some specific examples?
>
> PS. I am not trying to be difficult. I honestly don't understand the 
> use case yet, and the PEP doesn't do much to support it.

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