[Python-Dev] PEP 460 reboot

[Daniel Holth]

On Sun, Jan 12, 2014 at 9:18 PM, Guido van Rossum <guido at python.org> wrote:
> On Sun, Jan 12, 2014 at 6:07 PM, Daniel Holth <dholth at gmail.com> wrote:
>> Is there a formatting character that means "anything except a unicode
>> string" to prevent accidentally interpolating a Unicode string into a
>> bytes string without [a sane] encoding?
>
> No, and we shouldn't introduce one. An operation should either work
> for no type, one type, a few specific types, or all types. Something
> that works for all but one type will *appear* to work for all types to
> a casually experimenting user and may pass extensive unittests,
> leaving a bomb that can detonate when you least expect it.

That pretty much describes how I feel about str(bytes). I would accept
"only a bytes" or "only a string" as consolation formatting characters
:-)