Re: inconsistency in converting from/to hex
On 17/11/2013 06:31, Steven D'Aprano wrote: I agree that its a bit of a mess. But only a little bit, and it will be less messy by 3.5 when the codecs solution is re-introduced. Then the codecs.encode and decode functions will be the one obvious way. For anyone who's interested in the codecs issues see http://bugs.python.org/issue7475 and http://bugs.python.org/issue19543 -- Python is the second best programming language in the world. But the best has yet to be invented. Christian Tismer Mark Lawrence -- https://mail.python.org/mailman/listinfo/python-list
Re: inconsistency in converting from/to hex
17.11.13 08:31, Steven D'Aprano написав(ла):
There's already at least two ways to do it in Python 2:
py import binascii
py binascii.hexlify('Python')
'507974686f6e'
py import codecs
py codecs.encode('Python', 'hex')
'507974686f6e'
Third:
import base64
base64.b16encode(b'Python')
b'507974686F6E'
Fourth:
'%0*x' % (2*len(b'Python'), int.from_bytes(b'Python', byteorder='big'))
b'507974686F6E'
Fifth:
''.join('%02x' % b for b in b'Python')
b'507974686F6E'
[Aside: in Python 3, the codecs where (mistakenly) removed, but they'll
be added back in 3.4 or 3.5.]
Only renamed.
import codecs
codecs.encode(b'Python', 'hex_codec')
b'507974686f6e'
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inconsistency in converting from/to hex
We can convert from hex str to bytes with bytes.fromhex class method:
b = bytes.fromhex(ff)
But we cannot convert from hex binary:
b = bytes.fromhex(bff)
Traceback (most recent call last):
File stdin, line 1, in module
TypeError: must be str, not bytes
We don't have bytes_instance.tohex() instance method.
But we have binascii.hexlify. But binascii.hexlify does not return an
str. It returns a bytes instance instead.
import binascii
binascii.hexlify(b)
b'ff'
Its reverse function binascii.unhexlify can be used on str and bytes too:
binascii.unhexlify(b'ff')
b'\xff'
binascii.unhexlify('ff')
b'\xff'
Questions:
* if we have bytes.fromhex() then why don't we have bytes_instance.tohex() ?
* if the purpose of binascii.unhexlify and bytes.fromhex is the same,
then why allow binary arguments for the former, and not for the later?
* in this case, should there be one obvious way to do it or not?
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Re: inconsistency in converting from/to hex
On Saturday, November 16, 2013 5:16:58 PM UTC-5, Laszlo Nagy wrote:
We can convert from hex str to bytes with bytes.fromhex class method:
b = bytes.fromhex(ff)
But we cannot convert from hex binary:
b = bytes.fromhex(bff)
Traceback (most recent call last):
File stdin, line 1, in module
TypeError: must be str, not bytes
We don't have bytes_instance.tohex() instance method.
But we have binascii.hexlify. But binascii.hexlify does not return an
str. It returns a bytes instance instead.
import binascii
binascii.hexlify(b)
b'ff'
Its reverse function binascii.unhexlify can be used on str and bytes too:
binascii.unhexlify(b'ff')
b'\xff'
binascii.unhexlify('ff')
b'\xff'
Questions:
* if we have bytes.fromhex() then why don't we have bytes_instance.tohex() ?
* if the purpose of binascii.unhexlify and bytes.fromhex is the same,
then why allow binary arguments for the former, and not for the later?
* in this case, should there be one obvious way to do it or not?
The standard library is not always as consistent as we might like. I don't
think there is a better answer than that.
This will work if you want to use fromhex with bytes:
b = bytes.fromhex(bff.decode(ascii))
--Ned.
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Re: inconsistency in converting from/to hex
On Sat, 16 Nov 2013 23:16:58 +0100, Laszlo Nagy wrote:
Questions:
* if we have bytes.fromhex() then why don't we have
bytes_instance.tohex() ?
The Python core developers are quite conservative about adding new
methods, particularly when there is already a solution to the given
problem. bytes.fromhex is very useful, because when working with binary
data it is common to give data as strings of hex values, and so it is
good to have a built-in method for it:
image = bytes.fromhex('ffd8ffe000104a464946000101 ...')
On the other hand, converting bytes to hexadecimal values is less common.
There's already at least two ways to do it in Python 2:
py import binascii
py binascii.hexlify('Python')
'507974686f6e'
py import codecs
py codecs.encode('Python', 'hex')
'507974686f6e'
[Aside: in Python 3, the codecs where (mistakenly) removed, but they'll
be added back in 3.4 or 3.5.]
So I can only imagine that had somebody proposed a bytes.tohex() method,
they would have been told there's already a way to do that, this isn't
important enough to justify being built-in.
* if the purpose of binascii.unhexlify and bytes.fromhex is the same,
then why allow binary arguments for the former, and not for the later?
I would argue that the purpose is *not* the same. binascii is for working
with binary files, hence it accepts bytes and produces bytes.
bytes.fromhex is for producing bytes from strings.
It's an exceedingly narrow distinction, and I can understand anyone who
is not convinced by my argument. I'm only half-convinced myself.
* in this case, should there be one obvious way to do it or not?
Define it. Do you mean convert bytes to bytes, bytes to str, str
to bytes, or str to str?
Besides, one *obvious* way is not the same as *only one* way.
I agree that its a bit of a mess. But only a little bit, and it will be
less messy by 3.5 when the codecs solution is re-introduced. Then the
codecs.encode and decode functions will be the one obvious way.
--
Steven
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