reorder byte order in hex string (python)
Solution 1
array.arrays
have a byteswap method:
import binascii
import struct
import array
x = binascii.unhexlify('b62e000052e366667a66408d')
y = array.array('h', x)
y.byteswap()
s = struct.Struct('<Id')
print(s.unpack_from(y))
# (46638, 943.2999999994321)
The h
in array.array('h', x)
was chosen because it tells array.array
to regard the data in x
as an array of 2-byte shorts. The important thing is that each item be regarded as being 2-bytes long. H
, which signifies 2-byte unsigned short, works just as well.
Solution 2
This should do exactly what unutbu's version does, but might be slightly easier to follow for some...
from binascii import unhexlify
from struct import pack, unpack
orig = unhexlify('b62e000052e366667a66408d')
swapped = pack('<6h', *unpack('>6h', orig))
print unpack('<Id', swapped)
# (46638, 943.2999999994321)
Basically, unpack 6 shorts big-endian, repack as 6 shorts little-endian.
Again, same thing that unutbu's code does, and you should use his.
edit Just realized I get to use my favorite Python idiom for this... Don't do this either:
orig = 'b62e000052e366667a66408d'
swap =''.join(sum([(c,d,a,b) for a,b,c,d in zip(*[iter(orig)]*4)], ()))
# '2eb60000e3526666667a8d40'
Solution 3
The swap from 'data_string_in_orig' to 'data_string_in_swapped' may also be done with comprehensions without using any imports:
>>> d = 'b62e000052e366667a66408d'
>>> "".join([m[2:4]+m[0:2] for m in [d[i:i+4] for i in range(0,len(d),4)]])
'2eb60000e3526666667a8d40'
The comprehension works for swapping byte order in hex strings representing 16-bit words. Modifying it for a different word-length is trivial. We can make a general hex digit order swap function also:
def swap_order(d, wsz=4, gsz=2 ):
return "".join(["".join([m[i:i+gsz] for i in range(wsz-gsz,-gsz,-gsz)]) for m in [d[i:i+wsz] for i in range(0,len(d),wsz)]])
The input params are:
d : the input hex string
wsz: the word-size in nibbles (e.g for 16-bit words wsz=4, for 32-bit words wsz=8)
gsz: the number of nibbles which stay together (e.g for reordering bytes gsz=2, for reordering 16-bit words gsz = 4)
Wolfgang R.
Updated on July 13, 2022Comments
-
Wolfgang R. almost 2 years
I want to build a small formatter in python giving me back the numeric values embedded in lines of hex strings.
It is a central part of my formatter and should be reasonable fast to format more than 100 lines/sec (each line about ~100 chars).
The code below should give an example where I'm currently blocked.
'data_string_in_orig' shows the given input format. It has to be byte swapped for each word. The swap from 'data_string_in_orig' to 'data_string_in_swapped' is needed. In the end I need the structure access as shown. The expected result is within the comment.
Thanks in advance Wolfgang R
#!/usr/bin/python import binascii import struct ## 'uint32 double' data_string_in_orig = 'b62e000052e366667a66408d' data_string_in_swapped = '2eb60000e3526666667a8d40' print data_string_in_orig packed_data = binascii.unhexlify(data_string_in_swapped) s = struct.Struct('<Id') unpacked_data = s.unpack_from(packed_data, 0) print 'Unpacked Values:', unpacked_data ## Unpacked Values: (46638, 943.29999999943209) exit(0)
-
Kenan Banks over 11 years
array.byteswap
. Sweet. Guess I'll go ahead and not post the kludgy unpack big-endian / repack little-endian solution I had cooking... -
unutbu over 11 yearsGo ahead and post it! Having more than one way to solve a problem can be useful.
-
Wolfgang R. over 11 yearsThanks, this was fast and perfect for me. By the way 100k lines in 5 sec.
-
Kenan Banks over 11 years@WolfgangR. - if this solution worked for you, you should accept the answer.