introduce bytes.hex method (also for bytearray and memoryview)

[wiggin15]

BPO	9951
Nosy	@malemburg, @warsaw, @birkenfeld, @rhettinger, @terryjreedy, @gpshead, @mdickinson, @ncoghlan, @pitrou, @ericvsmith, @tiran, @merwok, @ethanfurman, @wiggin15, @vadmium, @serhiy-storchaka
Files	bytes.hex.diff bytes.hex-1.diff

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/gpshead'
closed_at = <Date 2015-04-26.05:07:16.157>
created_at = <Date 2010-09-25.23:38:47.004>
labels = ['interpreter-core', 'type-feature']
title = 'introduce bytes.hex method (also for bytearray and memoryview)'
updated_at = <Date 2015-11-10.17:19:10.649>
user = 'https://github.com/wiggin15'

bugs.python.org fields:

activity = <Date 2015-11-10.17:19:10.649>
actor = 'python-dev'
assignee = 'gregory.p.smith'
closed = True
closed_date = <Date 2015-04-26.05:07:16.157>
closer = 'gregory.p.smith'
components = ['Interpreter Core']
creation = <Date 2010-09-25.23:38:47.004>
creator = 'wiggin15'
dependencies = []
files = ['38961', '39204']
hgrepos = []
issue_num = 9951
keywords = ['patch']
message_count = 38.0
messages = ['117397', '118272', '132911', '190112', '193034', '193041', '197571', '199629', '199631', '199634', '199665', '205744', '226692', '226703', '226730', '226731', '226732', '226734', '226735', '226737', '226738', '226745', '226750', '227335', '240607', '240719', '242011', '242027', '242030', '242031', '242033', '242034', '242035', '242036', '242039', '242041', '242043', '254456']
nosy_count = 21.0
nosy_names = ['lemburg', 'barry', 'georg.brandl', 'rhettinger', 'terry.reedy', 'gregory.p.smith', 'mark.dickinson', 'ncoghlan', 'pitrou', 'eric.smith', 'gotgenes', 'christian.heimes', 'eric.araujo', 'Arfrever', 'BreamoreBoy', 'ethan.furman', 'wiggin15', 'python-dev', 'martin.panter', 'serhiy.storchaka', 'hct']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue9951'
versions = ['Python 3.5']

[wiggin15]

Following up on these discussions:
http://psf.upfronthosting.co.za/roundup/tracker/issue3532
http://www.gossamer-threads.com/lists/python/dev/863892

I'm submitting a patch to add bytes.hex method in accordance to PEP-358.
The code was taken from binascii so it should be "tested".
Also added bytearray.hex and fixed the documentation and testing.

There are additional things to discuss, for example:

• multiple and different implementations of tohex\fromhex - in binascii, sha1module, bytes, bytearray...
• binascii's functions which perform the same thing, but those functions and the rest of binascii's functions receive and return wrong types. I would fix this but it breaks compatibility.

[wiggin15]

fixed to Py_UNICODE

[rhettinger]

See also: bpo-11756

[terryjreedy]

Also bpo-3532

[wiggin15]

Hi, is there any chance to get this merged? This ticket has been open for almost 3 years...

[serhiy-storchaka]

There are several ways to do this: base64.b16encode, binascii.a2b_hex, hex(int.from_bytes(...)), etc. Why you need yet one?

[wiggin15]

You can follow the discussion I linked in the ticket description for an answer:
http://psf.upfronthosting.co.za/roundup/tracker/issue3532
Mainly the answer is: to conform to PEP-358 and to provide the opposite of bytes.fromhex.
I agree that you can use binascii, but apparently it was decided that this functionality is good to have in the builtins (what used to be encode/decode('hex') in Python 2.x, and what is now bytes.fromhex, with the missing bytes.hex). In addition, binascii works a little differently - already discussed in the given link...

[tiran]

I like to see the feature in 3.4, too.

[pitrou]

If it's the reverse of fromhex(), perhaps we should call it tohex()?

[tiran]

Funny thing. I was searching for "tohex" when I found this ticket.

[birkenfeld]

Blasphemous question: why not give bytes a __hex__ method? Then you could use hex() to convert them :)

The patch is outdated; it should not use PyUnicode_AS_UNICODE, but PyUnicode_New(..., 127) and then PyUnicode_1BYTE_DATA to get the char array.

[hct]

would be good if we can specify a optional flag to get all cap hex. currently, I have to do hexlify( some_bytes ).decode( 'UTF-8' ).upper(). would be good to be able to do some_bytes.hex( upper=1 )

[vstinner]

New features cannot be added to Python 2 anymore, only to the current development version which is now Python 3.5.

If new methods are added to bytes, they should be added to bytearray too. Maybe we should also consider add them to memoryview? memoryview has already a .bytes() method and can be casted to type "B" (array of integers in range 0..255).

The float type has .hex() and .fromhex() methods. We should kepe these names to stay consistent. Which kind of output do you prefer? "0xHH 0xHH ...", "HH HH HH ..." or "HHHHHH..."? Do you want to add parameters to choose the format?

Current binascii format:

>>> binascii.hexlify('abc')
'616263'