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~