[issue22385] Define a binary output formatting mini-language for *.hex()

[Gregory P. Smith]

Change by Gregory P. Smith :


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resolution:  -> fixed
stage: patch review -> commit review
status: open -> closed
versions: +Python 3.9 -Python 3.8

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[issue22385] Define a binary output formatting mini-language for *.hex()

[Gregory P. Smith]

Gregory P. Smith  added the comment:

thanks, i'll take care of them.

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[issue22385] Define a binary output formatting mini-language for *.hex()

[Karthikeyan Singaravelan]

Karthikeyan Singaravelan  added the comment:

This change seems to have created some compile time warnings : 
https://buildbot.python.org/all/#/builders/103/builds/2544/steps/3/logs/warnings__6_

Python/pystrhex.c:18:45: warning: passing argument 1 of ‘PyObject_Size’ 
discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
Python/pystrhex.c:60:27: warning: comparison of integer expressions of 
different signedness: ‘unsigned int’ and ‘Py_ssize_t’ {aka ‘const int’} 
[-Wsign-compare]
Python/pystrhex.c:90:29: warning: ‘sep_char’ may be used uninitialized in this 
function [-Wmaybe-uninitialized]
Python/pystrhex.c:90:29: warning: ‘sep_char’ may be used uninitialized in this 
function [-Wmaybe-uninitialized]

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[issue22385] Define a binary output formatting mini-language for *.hex()

[Gregory P. Smith]

Gregory P. Smith  added the comment:


New changeset 0c2f9305640f7655ba0cd5f478948b2763b376b3 by Gregory P. Smith in 
branch 'master':
bpo-22385: Support output separators in hex methods. (#13578)
https://github.com/python/cpython/commit/0c2f9305640f7655ba0cd5f478948b2763b376b3


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[issue22385] Define a binary output formatting mini-language for *.hex()

[Gregory P. Smith]

Gregory P. Smith  added the comment:

Given that we have f-strings, I don't think a format mini language makes as 
much sense.  My PR adds support for separators to the .hex() methods (and to 
binascii.hexlify) via a parameter.  Extending beyond what MicroPython already 
does in its binascii implementation (a single sep parameter).

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[issue22385] Define a binary output formatting mini-language for *.hex()

[Gregory P. Smith]

Change by Gregory P. Smith :


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keywords: +patch
pull_requests: +13486
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/13578

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[issue22385] Define a binary output formatting mini-language for *.hex()

[Gregory P. Smith]

Gregory P. Smith  added the comment:

FYI - micropython added an optional 'sep' second argument to binascii.hexlify() 
that is a single character separator to insert between every two hex digits.

given the #9951 .hex() methods we have everywhere (and corresponding .fromhex), 
binascii.hexlify is almost a legacy API.  (but micropython doesn't have those 
methods yet).  one key difference?  hexlify returns the hex value as a bytes 
rather than a str.

just adding a couple of parameters to the hex() method seems fine.  a separator 
string and a number of bytes to separate.

yet another minilanguage would be overkill.  and confusing in the face of the 
existing numeric formatting mini language ability to insert , or _ separators 
every four spaces ala f'{value:_x}'.

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stage:  -> needs patch
type:  -> enhancement
versions: +Python 3.8 -Python 3.7

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[issue22385] Define a binary output formatting mini-language for *.hex()

[STINNER Victor]

Changes by STINNER Victor :


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[issue22385] Define a binary output formatting mini-language for *.hex()

[Nick Coghlan]

Nick Coghlan added the comment:

Re-using an existing minilanguage to mean something completely different 
wouldn't be a good idea.

Whether or not we should add any bytes specific features for this at all is 
also still an open question, as one of the points raised in the latest 
python-ideas thread is that this may be better handled as a general purpose 
string splitting method that breaks the string up into fixed size units, which 
can then be rejoined with an arbitrary delimeter. For example:


>>> digit_groups = b'\xb9\x01\xef'.hex().splitgroups(2)
>>> ' '.join(digit_groups)
'b9 01 ef'

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[issue22385] Define a binary output formatting mini-language for *.hex()

[Robert]

Robert added the comment:

regarding the proposal for mini format languages for bytes (msg292663):
Wouldn't it be more consistent if the format specifiers are identical to the 
one of int's (see 
https://docs.python.org/3/library/string.html#format-specification-mini-language).

I.e. "X" / "x" for hex, "o" for octal, "d" for decimal, "b" for binary, "c" for 
character (=default). Only 'A' need to be added for printing only ascii 
characters.

Furthermore I cannot see in how far the format spec in 
http://bugs.python.org/issue22385#msg292663 ("h#,1") is more intuitive than in 
http://bugs.python.org/issue22385#msg226733 ("#,.4x"), which looks like the 
existing minilang.

Why does Python need a new format mini lang, if the existing one provides most 
of the requirements. As developer it is already hard to memorize the details of 
the existing minilang. Ideally I do not need to learn a similar but different 
one for bytes...

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[issue22385] Define a binary output formatting mini-language for *.hex()

[Nick Coghlan]

Nick Coghlan added the comment:

Minimalist proposal:

def hex(self, *, bytes_per_group=None, delimiter=" "):
"""B.hex() -> string of hex digits
B.hex(bytes_per_group=N) -> hex digits in groups separated by 
*delimeter*

Create a string of hexadecimal numbers from a bytes object::

>>> b'\xb9\x01\xef'.hex()
'b901ef'
>>> b'\xb9\x01\xef'.hex(bytes_per_group=1)
'b9 01 ef'
"""

Alternatively, the grouping could be by digit rather than by byte:

def hex(self, *, group_digits=None, delimiter=" "):
"""B.hex() -> string of hex digits
B.hex(group_digits=N) -> hex digits in groups separated by *delimeter*

Create a string of hexadecimal numbers from a bytes object::

>>> b'\xb9\x01\xef'.hex()
'b901ef'
>>> b'\xb9\x01\xef'.hex(group_digits=2)
'b9 01 ef'
"""

One potential advantage of the `group_digits` approach is that it could be 
fairly readily adapted to the hex/oct/bin builtins (although if we did that, it 
would make the lack of a "dec" builtin for decimal formatting a bit weird)

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[issue22385] Define a binary output formatting mini-language for *.hex()

[Eric V. Smith]

Eric V. Smith added the comment:

The Unix "od" command pretty much has all of the possibilities covered.

https://linuxconfig.org/od-1-manual-page

Although "named characters" might be going a bit far. Float, too.

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[issue22385] Define a binary output formatting mini-language for *.hex()

[Gregory P. Smith]

Gregory P. Smith added the comment:

Based on the ideas thread it isn't obvious that chunk size means "per byte".  I 
suggest either specifying the number of base digits per delimiter.  Or using a 
name other than chunk that indicates it means bytes.

If we're going to do this, it should also be done for octal formatting (the 'o' 
code) for consistency.

Also, per the python-ideas thread, via parameters to the .hex() method on 
bytes/bytearray/memoryview.

I'm inclined to leave 'A' printable-ascii formatting out.  Or at least consider 
that it could also work on unicode str.

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[issue22385] Define a binary output formatting mini-language for *.hex()

[Nick Coghlan]

Nick Coghlan added the comment:

Copying the amended proposal from that python-ideas thread into here:

Start with a leading base format character (chosen to be orthogonal to the 
default format characters):

"h": lowercase hex
"H": uppercase hex
"A": ASCII (using "." for unprintable & extended ASCII)

format(b"xyz", "A") -> 'xyz'
format(b"xyz", "h") -> '78797a'
format(b"xyz", "H") -> '78797A'

Followed by a separator and "chunk size":

format(b"xyz", "h 1") -> '78 79 7a'
format(b"abcdwxyz", "h 4") -> '61626364 7778797a'

format(b"xyz", "h,1") -> '78,79,7a'
format(b"abcdwxyz", "h,4") -> '61626364,7778797a'

format(b"xyz", "h:1") -> '78:79:7a'
format(b"abcdwxyz", "h:4") -> '61626364:7778797a'

In the "h" and "H" cases, allow requesting a preceding "0x" on the chunks:

format(b"xyz", "h#") -> '0x78797a'
format(b"xyz", "h# 1") -> '0x78 0x79 0x7a'
format(b"abcdwxyz", "h# 4") -> '0x61626364 0x7778797a'

In the thread, I suggested the section before the format character would use 
the standard string formatting rules (alignment, fill character, width, 
precision), but I now think that would be ambiguous and confusing, and would be 
better left as a post-processing step on the rendered text.

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[issue22385] Define a binary output formatting mini-language for *.hex()

[Christian H]

Changes by Christian H :


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[issue22385] Define a binary output formatting mini-language for *.hex()

[Nick Coghlan]

Nick Coghlan added the comment:

Reviewing the items I had flagged as dependencies of issue 22555 for personal 
tracking purposes, I suggest we defer further consideration of this idea to 3.6 
after folks have had a chance to get some experience with the basic bytes.hex() 
method.

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[issue22385] Define a binary output formatting mini-language for *.hex()

[Barry A. Warsaw]

Changes by Barry A. Warsaw ba...@python.org:


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[issue22385] Define a binary output formatting mini-language for *.hex()

[Alexander Belopolsky]

Changes by Alexander Belopolsky alexander.belopol...@gmail.com:


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[issue22385] Define a binary output formatting mini-language for *.hex()

[Nick Coghlan]

Nick Coghlan added the comment:

Retitled the issue and made it depend on issue 9951.

I now think it's better to tackle this more like strftime and have a method 
that accepts of particular custom formatting mini-language (in this case, the 
new hex() methods proposed in issue 9951), and then also support that 
mini-language in the __format__() method.

It would likely need a PEP to decide on the exact details of the formatting.

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dependencies: +introduce bytes.hex method
title: Allow 'x' and 'X' to accept bytes-like objects in string formatting - 
Define a binary output formatting mini-language for *.hex()

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[issue22385] Define a binary output formatting mini-language for *.hex()

[Nick Coghlan]

Nick Coghlan added the comment:

python-ideas post with a sketch of a possible mini-language: 
https://mail.python.org/pipermail/python-ideas/2014-September/029352.html

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