[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Xiang Zhang]

Xiang Zhang added the comment:


New changeset faa2cc63e45bc7d7ffab84bebe5a9f4fe065bd96 by Xiang Zhang in branch 
'3.6':
bpo-28856: Let %b format for bytes support objects that follow the buffer 
protocol  (GH-664)
https://github.com/python/cpython/commit/faa2cc63e45bc7d7ffab84bebe5a9f4fe065bd96


--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Xiang Zhang]

Xiang Zhang added the comment:


New changeset 7e2a54cdd977078b40b82182e46b201f8163f659 by Xiang Zhang in branch 
'master':
bpo-28856: Let %b format for bytes support objects that follow the buffer 
protocol (GH-546)
https://github.com/python/cpython/commit/7e2a54cdd977078b40b82182e46b201f8163f659


--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Larry Hastings]

Changes by Larry Hastings :


--
pull_requests: +582

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Xiang Zhang]

Xiang Zhang added the comment:

I committed the suboptimal patch. I close this issue now and if there is any 
enhancement solution, let's make it another issue. Thank you all.

--
resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed
versions:  -Python 3.5

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Following example copies the entire buffer object while copying only smart part 
is needed:

m = memoryview(b'x'*10**6)
b'%.100b' % m

I don't know whether this is important use case that is worth an optimization. 
The workaround is using slicing rather than truncating in format:

b'%b' % m[:100]

Or in the case of general buffer object:

b'%b' % memoryview(m).cast('B')[:100]

But in that case it is not hard to add an explicit conversion to bytes.

b'%b' % bytes(memoryview(m).cast('B')[:100])

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Xiang Zhang]

Changes by Xiang Zhang :


--
pull_requests: +546

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

@xiang.zhang - I am the OP for this issue, so naturally I expect this to be 
fixed.  I have a work-around in place for my own code, so I have no opinion on 
the particular versions.  I guess the normal policy on bug fixes should apply.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Ethan Furman]

Ethan Furman added the comment:

I suspect it was a simple oversight, and should be added now.  Since it's been 
missing for so long I think we should put it in 3.7, maybe put it in 3.6 (maybe 
not, since it has two point releases out now), but definitely not in 3.5.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Sometimes the implementation can expose drawbacks of initial design. I don't 
know whether there was good reason for omitting the support of the buffer 
protocol (in that case the PEP should be updated) or this is just an oversign. 
We should ask Ethan about this.

The change proposed by Xiang looks correct, but not very efficient. It makes 
one redundant copy of the data. More efficient implementation will complicate 
the code, and that can hit the performance of other cases.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Xiang Zhang]

Xiang Zhang added the comment:

What's your opinions Alexander and Ethan?

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Stefan Krah]

Stefan Krah added the comment:

For '%b', it looks like the PEP supports it. I didn't follow the PEP 
discussions, I think Ethan will know more.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Xiang Zhang]

Xiang Zhang added the comment:

Isn't this a discussed behaviour that is explicitly documented in PEP 461?

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

printf-style bytes formatting was added mainly for increasing compatibility 
with Python 2. It was restricted to support mostly features existing in Python 
2.

'%s' formatting in Python 3 supports bytes-like objects partially:

>>> b'%s' % array('B', [1, 2])
"array('B', [1, 2])"
>>> b'%s' % buffer(array('B', [1, 2]))
'\x01\x02'
>>> b'%s' % memoryview(array('B', [1, 2]))
Traceback (most recent call last):
  File "", line 1, in 
TypeError: cannot make memory view because object does not have the buffer 
interface
>>> b'%s' % bytearray(b'abc')
'abc'
>>> b'%s' % buffer(bytearray(b'abc'))
'abc'
>>> b'%s' % memoryview(bytearray(b'abc'))
''

I don't know whether there is a need of supporting the buffer protocol in 
printf-style bytes formatting. bytearray is already supported, buffer() doesn't 
exist in Python 3, memoryview() is not supported in Python 2. Seems this 
doesn't add anything for increasing the compatibility.

--
nosy: +skrah

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Xiang Zhang]

Changes by Xiang Zhang :


--
pull_requests: +449

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Xiang Zhang]

Changes by Xiang Zhang :


--
components: +Interpreter Core
stage: test needed -> patch review
versions: +Python 3.5, Python 3.6, Python 3.7

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Xiang Zhang]

Changes by Xiang Zhang :


--
nosy: +xiang.zhang

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


--
nosy: +ethan.furman, serhiy.storchaka

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue28856] %b format for bytes does not support objects that follow the buffer protocol

[Alexander Belopolsky]

New submission from Alexander Belopolsky:

Python 3.7.0a0 (default:be70d64bbf88, Dec  1 2016, 21:21:25)
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.42.1)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from array import array
>>> a = array('B', [1, 2])
>>> b'%b' % a
Traceback (most recent call last):
  File "", line 1, in 
TypeError: %b requires bytes, or an object that implements __bytes__, not 
'array.array'
>>> m = memoryview(a)
>>> b'%b' % m
Traceback (most recent call last):
  File "", line 1, in 
TypeError: %b requires bytes, or an object that implements __bytes__, not 
'memoryview'

Accorfing to documentation [1] objects that follow the buffer protocol should 
be supported.  Both array.array and memoryview follow the buffer protocol.

[1]: 
https://docs.python.org/3/library/stdtypes.html#printf-style-bytes-formatting


See also issue 20284 and PEP 461.

--
messages: 282215
nosy: belopolsky
priority: normal
severity: normal
stage: test needed
status: open
title: %b format for bytes does not support objects that follow the buffer 
protocol
type: behavior

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com