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~
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