Bitwise operations on byte string and int

Question

i am in the process of converting some cython code to python, and it went well until i came to the bitwise operations. Here is a snippet of the code:

in_buf_word = b'\xff\xff\xff\xff\x00'
bits = 8
in_buf_word >>= bits

If i run this it will spit out this error:

TypeError: unsupported operand type(s) for >>=: 'str' and 'int'

how would i fix this?

• Jongware: What is your expected outcome for that? Is that 8 a fixed amount, or could it be 2, 29, 33, or -1?
• Emil Bengtsson: bits is not a fixed amount, but in my case it is usually 8, however in_buf_word is the thing that would be sort of dynamic.

Answer 1

import bitstring
in_buf_word = b'\xff\xff\xff\xff\x00'
bits = 8
in_buf_word = bitstring.BitArray(in_buf_word ) >> bits

If you dont have it. Go to your terminal

pip3 install bitstring --> python 3
pip install bitstring --> python 2

To covert it back into bytes use the tobytes() method:

print(in_buf_word.tobytes())

• Emil Bengtsson: how would i convert it back to bytes ?
• Jackson: @EmilBengtsson use tobytes(). see edited answer for example

Answer 2

Shifting to the right by 8 bits just means cutting off the rightmost byte.

Since you already have a bytes object, this can be done more easily:

in_buf_word = in_buf_word[:-1]

Answer 3

You can do it by converting the bytes into an integer, shifting that, and then converting the result back into a byte string.

in_buf_word = b'\xff\xff\xff\xff\x00'
bits = 8
print(in_buf_word) # -> b'\xff\xff\xff\xff\x00'
temp = int.from_bytes(in_buf_word, byteorder='big') >> bits
in_buf_word = temp.to_bytes(len(in_buf_word), byteorder='big')
print(in_buf_word) # -> b'\x00\xff\xff\xff\xff'