how to write array of bits into a file using bytearray

Question

I have an array of int values range 0 to 1. ie [0,1,1,0,0,1,0,0,1...]. How can I use bytearray to write this into a file whereby each byte contains 8 elements in the array (8 bits). | and byte heading are only for example:

Output:

| byte 1 | byte 2 | etc...
|01100100|1...    |

011001001...

@KennyOstrom the first link is irrelevant and none of the answers in those links demonstrate how to solve my question using bytearray — llamaro25, Jun 06 '20 at 17:02
Huh, I wonder what the best way is. I guess one could do it in chunks of bytes. I couldn't find anything in the `struct` module for this. — Mateen Ulhaq, Jun 06 '20 at 17:11

Hoxha Alban · Answer 1 · 2020-06-06T17:48:31.417

Here there is an over engineered solution that works only when the list has a number of elements multiple of 8

l = [0,1,1,0,1,1,0,0,
     1,0,1,0,1,1,1,0,
     0,1,0,1,0,1,0,1,
     0,0,1,1,0,0,0,0]

for n in range(len(l)//8):
    print('| byte ', n+1, ' ', sep='', end='')

print('|')

for byte in zip(*[iter(l)]*8):
    print('|', *byte, sep='', end='')

print('|')

out:

| byte 1 | byte 2 | byte 3 | byte 4 |
|01101100|10101110|01010101|00110000|

score 0 · Accepted Answer · answered Jun 11 '20 at 13:26

Since I must post my own code, here we go.

arr = [0,1,1,0,1,1,1,0,1] 

bytearr = bytearray()
x = ''
for i in range(len(arr)):
    if i > 0 and i % 8 == 0:
        bytearr.append(int(x,2))
        x = str(arr[i])
    else:
        x += str(arr[i])

# handle remaining bits
if x != '':
    bytearr.append(int(x,2))

score -1 · Answer 3 · answered Jun 10 '20 at 22:27

You should post your own code, not ask someone to write it for you, and you were mean to me. But it sounds like a useful question for other people to look up, so here you go:

(a week late, just in case this was homework)

# helper function with some basic math
def number(digits, base):
    value = 0
    for digit in digits:
        value *= base
        value += int(digit)
    return value

if 826 != number('826', 10):
    raise ValueError

if 64+16+2+1 != number([0, 1, 0, 1, 0, 0, 1, 1], 2):
    raise ValueError

# helper function to break the data up into the expected chunks
# https://stackoverflow.com/a/312464/1766544
def chunks(arbitrary_list, chunk_size):
    for i in range(0, len(arbitrary_list), chunk_size):
        yield arbitrary_list[i:i + chunk_size]

data = [
    0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 1,
    0, 0, 0, 0, 0, 0, 1, 0,
    0, 0, 0, 0, 0, 1, 0, 0,
    0, 0, 0, 0, 1, 0, 0, 0,
    0, 0, 0, 1, 0, 0, 0, 0,
    0, 0, 1, 0, 0, 0, 0, 0,
    0, 1, 0, 0, 0, 0, 0, 0,
    1, 0, 0, 0, 0, 0, 0, 0,
]

# the bytearray constructor needs an iterable
# the iterable needs to yield the number
# the number needs 8 bits at a time
binary_data = bytearray((number(bits, base=2) for bits in chunks(data, 8)))

# write the bytearray to a file is too easy
# there's already a function that writes stuff to a file
#with open ('filename.data', 'wb') as f:
    #f.write(binary_data)

# but easier to demonstrate that we have the right values like so:
for n in binary_data:
    print(n)

output:

0
1
2
4
8
16
32
64
128

mean to you? go cry to mummy. take some criticism that your links weren't useful and move on. maybe don't stay on the site if your intention isn't to help — llamaro25, Jun 11 '20 at 13:18
also fyi number isn't a function. ```name 'number' is not defined``` — llamaro25, Jun 11 '20 at 13:39

how to write array of bits into a file using bytearray

3 Answers3