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

[Guido van Rossum]

Much better, but I'm still not happy with including %s at all. Otherwise
it's accept-worthy. (How's that for pressure. :-)


On Thu, Mar 27, 2014 at 11:04 AM, Ethan Furman <ethan at stoneleaf.us> wrote:

> On 03/27/2014 10:55 AM, Ethan Furman wrote:
>
>> On 03/27/2014 10:29 AM, Guido van Rossum wrote:
>>
>>>
>>> I also don't understand why we can't use %b instead of %s. AFAIK %b
>>> currently doesn't mean anything and I somehow don't
>>> expect we're likely to add it for other reasons (unless there's a
>>> proposal I'm missing?). Just like we use %a instead of
>>> %r to remind people that it's not quite the same (since it applies
>>> .encode('ascii', 'backslashreplace')), shouldn't we
>>> use anything *but* %s to remind people that that is also not the same
>>> (not at all, in fact)? The PEP's argument against
>>> %b ("rejected as not adding any value either in clarity or simplicity")
>>> is hardly a good reason.
>>>
>>
>> The biggest reason to use %s is to support a common code base for 2/3
>> endeavors.  The biggest reason to not include %b
>> is that it means binary number in format(); given that each type can
>> invent it's own mini-language, this probably isn't
>> a very strong argument against it.
>>
>> I have moderate feelings for keeping %s as a synonym for %b for backwards
>> compatibility with Py2 code (when it's
>> appropriate).
>>
>
> Changed to:
> ------------------------------------------------------------
> ----------------------
> ``%b`` will insert a series of bytes.  These bytes are collected in one of
> two
> ways:
>
>   - input type supports ``Py_buffer`` [4]_?
>
>     use it to collect the necessary bytes
>
>   - input type is something else?
>     use its ``__bytes__`` method [5]_ ; if there isn't one, raise a
> ``TypeError``
>
> In particular, ``%b`` will not accept numbers nor ``str``.  ``str`` is
> rejected
> as the string to bytes conversion requires an encoding, and we are
> refusing to
> guess; numbers are rejected because:
>
>   - what makes a number is fuzzy (float? Decimal? Fraction? some user
> type?)
>
>   - allowing numbers would lead to ambiguity between numbers and textual
>     representations of numbers (3.14 vs '3.14')
>
>   - given the nature of wire formats, explicit is definitely better than
> implicit
>
> ``%s`` is included as a synonym for ``%b`` for the sole purpose of making
> 2/3 code
> bases easier to maintain.  Python 3 only code should use ``%b``.
>
> Examples::
>
>     >>> b'%b' % b'abc'
>     b'abc'
>
>     >>> b'%b' % 'some string'.encode('utf8')
>     b'some string'
>
>     >>> b'%b' % 3.14
>
>     Traceback (most recent call last):
>     ...
>     TypeError: b'%b' does not accept 'float'
>
>     >>> b'%b' % 'hello world!'
>
>     Traceback (most recent call last):
>     ...
>     TypeError: b'%b' does not accept 'str'
> ------------------------------------------------------------
> ----------------------
>
>
> --
> ~Ethan~
> _______________________________________________
> Python-Dev mailing list
> Python-Dev at python.org
> https://mail.python.org/mailman/listinfo/python-dev
> Unsubscribe: https://mail.python.org/mailman/options/python-dev/
> guido%40python.org
>



-- 
--Guido van Rossum (python.org/~guido)
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-dev/attachments/20140327/c9dcf0ad/attachment.html>