Save a string of ones and zeros as those ones and zeros in binary using Python.

save_bits.py

import random
from io import StringIO

def write_bitstream(fname, bits):
    # bits are a string of ones and zeros, based on this
    # stackoverflow answer: https://stackoverflow.com/a/16888829/6938913
    # was broken due to utf-8 encoding using up to 4 bytes: https://stackoverflow.com/a/33349765/6937913
    sio = StringIO(bits)
    with open(fname, 'wb') as f:
        while 1:
            # Grab the next 8 bits
            b = sio.read(8)
            # Bail if we hit EOF
            if not b:
                break
            # If we got fewer than 8 bits, pad with zeroes on the right
            if len(b) < 8:
                b = b + '0' * (8 - len(b))
            # Convert to int
            i = int(b, 2)
            # Write
            f.write(i.to_bytes(1, byteorder='big'))

if __name__ == '__main__':
    # generate a string of just zeros and ones
    random.seed(0)
    s = list("0"*1000 + "1"*1000)
    random.shuffle(s)
    s = "".join(s)
    print(len(s)/8)
    write_bitstream("bits", s)

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