[Python-Dev] PEP 461 - Adding % and {} formatting to bytes (original) (raw)
Jan Kaliszewski zuo at chopin.edu.pl
Thu Jan 16 23:06:37 CET 2014
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16.01.2014 17:33, Michael Urman wrote:
On Thu, Jan 16, 2014 at 8:45 AM, Brett Cannon <brett at python.org> wrote:
Fine, if you're worried about bytes.format() overstepping by implicitly calling str.encode() on the return value of format() then you will need bytes_format() to get equivalent support. Could we just re-use PEP-3101's note (easily updated for Python 3): Note for Python 2.x: The 'formatspec' argument will be either a string object or a unicode object, depending on the type of the original format string. The format method should test the type of the specifiers parameter to determine whether to return a string or unicode object. It is the responsibility of the format method to return an object of the proper type. If format receives a formatspec of type bytes, it should return bytes. For such cases on objects that cannot support bytes (i.e. for str), it can raise. This appears to avoid the need for additional methods. (As does Nick's proposal of leaving it out for now.)
-1.
I'd treat the format()+.format()+str.format()-"ecosystem" as a nice text-data-oriented, complete Py3k feature, backported to Python 2 to share the benefits of the feature with it as well as to make the 2-to-3 transition a bit easier.
IMHO, the PEP-3101's note cited above just describes a workaround over the flaws of the Py2's obsolete text model. Moving such complications into Py3k would make the feature (and especially the ability to implement your own .format()) harder to understand and make use of -- for little profit.
Such a move is not needed for compatibility. And, IMHO, the format()/format()/str.format()-matter is all about nice and flexible text formatting, not about binary data interpolation.
16.01.2014 10:56, Nick Coghlan wrote:
I have a different proposal: let's just add mod formatting to bytes, and leave the extensible formatting system as a text only operation.
We don't really care if bytes supports that method for version compatibility purposes, and the deliberate flexibility of the design makes it hard to translate into the binary domain. So let's just not provide that - let's accept that, for the binary domain, printf style formatting is just a better fit for the job :)
+1!
However, I am not sure if %s should be limited to bytes-like objects. As "practicality beats purity", I would be +0.5 for enabling the following:
input type supports Py_buffer? use it to collect the necessary bytes
input type has the bytes() method? use it to collect the necessary bytes
input type has the encode() method? raise TypeError
otherwise: use something equivalent to ascii(obj).encode('ascii') (note that it would nicely format numbers + format other object in more-or-less useful way without the fear of encountering a non-ascii data).
another option: use str()-representation of strictly defined types, e.g.: int, float, decimal.Decimal, fractions.Fraction...
Cheers. *j
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