Decode Hex String in Python 3

66
votes

In Python 2, converting the hexadecimal form of a string into the corresponding unicode was straightforward:

comments.decode("hex")

where the variable 'comments' is a part of a line in a file (the rest of the line does not need to be converted, as it is represented only in ASCII.

Now in Python 3, however, this doesn't work (I assume because of the bytes/string vs. string/unicode switch. I feel like there should be a one-liner in Python 3 to do the same thing, rather than reading the entire line as a series of bytes (which I don't want to do) and then converting each part of the line separately. If it's possible, I'd like to read the entire line as a unicode string (because the rest of the line is in unicode) and only convert this one part from a hexadecimal representation.

3
pythonpython-3.x
I'm not sure that hex encoding strings makes all that much sense. If you want to store an incompatible encoding I'd at least use base 64 because it is more efficient. That doesn't invalidate the question / answer in any way of course, maybe somebody else decided upon hex. - Maarten Bodewes

3 Answers

110
votes

Something like:

>>> bytes.fromhex('4a4b4c').decode('utf-8')
'JKL'

Just put the actual encoding you are using.

19
votes
import codecs

decode_hex = codecs.getdecoder("hex_codec")

# for an array
msgs = [decode_hex(msg)[0] for msg in msgs]

# for a string
string = decode_hex(string)[0]
-1
votes

The answers from @unbeli and @Niklas are good, but @unbeli's answer does not work for all hex strings and it is desirable to do the decoding without importing an extra library (codecs). The following should work (but will not be very efficient for large strings):

>>> result = bytes.fromhex((lambda s: ("%s%s00" * (len(s)//2)) % tuple(s))('4a82fdfeff00')).decode('utf-16-le')
>>> result == '\x4a\x82\xfd\xfe\xff\x00'
True

Basically, it works around having invalid utf-8 bytes by padding with zeros and decoding as utf-16.