Little to big endian buffer at once python

Question

I've created a buffer of words represented in little endian(Assuming each word is 2 bytes):

A000B000FF0A

I've separated the buffer to 3 words(2 bytes each)

A000
B000
FF0A

and after that converted to big endian representation:

00A0
00B0
0AFF

Is there a way instead of split into words to represent the buffer in big endian at once? Code:

buffer='A000B000FF0A'
for i in range(0, len(buffer), 4):
    value = endian(int(buffer[i:i + 4], 16))

def endian(num):
    p = '{{:0{}X}}'.format(4)
    hex = p.format(num)
    bin = bytearray.fromhex(hex).reverse()
    l = ''.join(format(x, '02x') for x in bin)
    return int(l, 16)

I am not sure I have understood your question. Python does not have natively an unsigned int. Ref: https://stackoverflow.com/questions/20766813/how-to-convert-signed-to-unsigned-integer-in-python#:~:text=on%20this%20post.-,Python%20doesn't%20have%20builtin%20unsigned%20types.,fixed%2Dbyte%2Dsize%20integer. — Fra93, Oct 06 '22 at 09:55
Can you show us the code you wrote to achieve the results you have in your post? — Fra93, Oct 06 '22 at 09:56
I don't really understand what you are trying to do, but Numpy can do that sort of thing easily and fast https://numpy.org/doc/stable/user/basics.byteswapping.html Or you could look at `struct.unpack()` — Mark Setchell, Oct 06 '22 at 10:07

ukBaz · Accepted Answer · 2022-10-06T10:40:40.700

Using the struct or array libraries are probably the easiest ways to do this.

Converting the hex string to bytes first is needed.

Here is an example of how it could be done:

from array import array
import struct

hex_str = 'A000B000FF0A'
raw_data = bytes.fromhex(hex_str)
print("orig string:      ", hex_str.casefold())
# With array lib
arr = array('h')
arr.frombytes(raw_data)
# arr = array('h', [160, 176, 2815])
arr.byteswap()
array_str = arr.tobytes().hex()
print(f"Swap using array: ", array_str)

# With struct lib
arr2 = [x[0] for x in struct.iter_unpack('<h', raw_data)]
# arr2 = [160, 176, 2815]
struct_str = struct.pack(f'>{len(arr2) * "h"}', *arr2).hex()
print("Swap using struct:", struct_str)

Gives transcript:

orig string:       a000b000ff0a
Swap using array:  00a000b00aff
Swap using struct: 00a000b00aff

score 1 · Answer 2 · answered Oct 06 '22 at 10:19

You can use the struct to interpret your bytes as big or little endian. Then you can use the hex() method of the bytearray object to have a nice string representation.

Docs for struct.

import struct

# little endian
a = struct.pack("<HHH",0xA000,0xB000,0xFF0A) 

# bih endian
b = struct.pack(">HHH",0xA000,0xB000,0xFF0A) 

print(a)
print(b)

# convert back to string
print( a.hex()  )
print( b.hex() )

Which gives:

b'\x00\xa0\x00\xb0\n\xff'
b'\xa0\x00\xb0\x00\xff\n'
00a000b00aff
a000b000ff0a

Little to big endian buffer at once python

2 Answers2