[Python-ideas] bitwise operations on bytes

[Facundo Batista]

On Sat, Aug 8, 2009 at 6:31 PM, Guido van Rossum<guido at python.org> wrote:

> In the grander scheme of things, I worry that interpreting byte
> strings as integers and implementing bitwise operators on them is
> going to cause more confusion and isn't generally useful enough to

Indeed.  But let me rephrase this.

I don't know Python, I'm just starting with Py3k, and I see a bytes
object. I don't know what a "byte string" is  (and I even feel that
the term is strange), but I understand that b"b3\xdd" is an array of
three bytes, which, of course, is an array of 24 bits (unless I know
that bytes are not always octets, but I think it's the same for this
case).

So, I think that providing bit semantics is a must for bytes objects.

I don't care (or I don't know enough to know that this exist) about
big/little endian, I just assume that this "just works" (it's is the
same case with line ending bytes: I may not know that different OSs
finish lines with different marks).

*I* (me as Facundo), don't really know enough to be able to propose
"what could work and keep surprise to a minimum", but just wanted to
present an "end user case" about this.


> warrant the extra code. I'd be okay with a standard API to transform a
> byte array into an integer and vice versa -- there you can be explicit
> about byte order and what to do about negative numbers. I can't

Yes. Bit arrays and integers suffer (suffer?) from the same issue that
Unicode. An integer, and an Unicode character, are encoded into
bits... and if you have bits, you need to know how to decode them to
get again your Unicode character, or your integer.

Maybe we could use the same names? What about something like b"....".
decode("little_endian__two's_complement") --> int?  (please, very
please, better encoding names)


Regards,

-- 
.    Facundo

Blog: http://www.taniquetil.com.ar/plog/
PyAr: http://www.python.org/ar/