#StackBounty: #python #type-conversion #byte #bit Convert integer to half-byte, `to_bytes()`?

Bounty: 50

I have a list of integers:

var = [1, 5, 4, 17, 231, 89]

If I wanted to convert it to a list of bytes instead, I can do:

[(i).to_bytes(1, byteorder='big') for i in var]

Since each value in var is less than 256, it can fit in one byte per integer. But if I had another list, say:

var = [1, 2, 15, 12]

This can fit an integer into half a byte, or more accurate to what I’m looking for, fit two integers per byte.

How can I specify to combine two integers into a byte if possible, both to and from?

Something like below:

var1 = [1, 5, 4, 17, 231, 89]
var2 = [1, 2, 15, 12]

def foo(var):
  if max(var) < 2**4:
    num_bytes = 0.5
  elif max(var) < 2**8:
    num_bytes = 1
  elif max(var) < 2**16:
    num_bytes = 2

  if num_bytes >= 1:
    return [(i).to_bytes(num_bytes, byteorder='big') for i in var], num_bytes
  elif num_bytes = 0.5:
    # convert var to list of nybbles
    # combine two nybbles to a byte
    # create list of bytes (length is half length of var)
    # return it and num_bytes

def unfoo(var, num_bytes):
  if num_bytes >= 1:
    print([int.from_bytes(i, 'big') for i in var])
  elif num_bytes = 0.5:
    # print original list of integers again

I want to convert a list of integers into a list of bytes, but fitting two nybbles to a byte if it can fit, then do the conversion back.

Desired outcome is:

a, b = foo(var1)
unfoo(a, b) # prints [1, 5, 4, 17, 231, 89]

a, b = foo(var2)
unfoo(a, b) # prints [1, 2, 15, 12]

I don’t want a list of smallest number of bits to represent a single number. Note the max(list): if all values in the list can be 8-bits, fit it to 8-bits; if all values can be 16-bits, fit it to 16-bits; if all values can be a nybble, then make two nybble pairs into a list of bytes.

Basically if I have two integers that can fit in a nybble each, how do I concatenate both into a single byte? If I know that bytes need to be split into two, how can I do the split? I can always assume the original list will be divisible by 2.


Get this bounty!!!

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