[Python-Dev] Adding bytes.frombuffer() constructor to PEP 467

[Chris Barker - NOAA Federal]

>   This is what happens with numpy arrays:
>
> >>> bytes(numpy.array([2], 'i1'))
> b'\x00\x00'
>
> >>> bytes(numpy.array([2, 2], 'i1'))
> b'\x02\x02'
>
> For better or worse, single-element numpy arrays have a working __index__ methods

Ouch -- that probably is for the worse..

There are Numpy scalars that should be used for that.


> 1. For 3.6, restore and document 3.5 behavior.  Recommend that 3rd party types that are both integer-like and buffer-like implement their own __bytes__ method to resolve the bytes(x) ambiguity.

+1 -- though the default should be clear if there isn't one.

> 2.1.  Accept only objects with a __bytes__ method or a sequence of ints in range(256).

If frombuffer() is added, then yes.

> 2.2.  Expand __bytes__ definition to accept optional encoding and errors parameters.  Implement str.__bytes__(self, [encoding[, errors]]).

Ouch! I understand the desire to keep a simple API -- but I think
encoding clearly belongs with the strong object. What's wrong with:

s.encode() ?

IIUC, the ONLY object one could possibly encode anyway is a string -
'cause you have to know the internal representation. So bytes() would
simply be passing the encoding info off to the string anyway ( or
other object with and encode method).

> 2.3.  Implement new specialized bytes.fromsize and bytes.frombuffer constructors as per PEP 467 and Inada Naoki proposals.

Maybe not important -- but nice to have a obvious and perform any way
to do it. ( does this proposal allow an initializing value?).

For prior art, Numpy has:

zeros()
ones()
empty()

And I would like to see an explicit frombuffer() constructor. See
others' notes about how using an intermediary memoryview is not
obvious and straightforward.

-CHB