Convert string to list of bits and viceversa

Question

I need to convert an ASCII string into a list of bits and vice versa:

str = "Hi" -> [0,1,0,0,1,0,0,0,0,1,1,0,1,0,0,1]

[0,1,0,0,1,0,0,0,0,1,1,0,1,0,0,1] -> "Hi"

Answer 1

There are many ways to do this with library functions. But I am partial to the third-party bitarray module.

>>> import bitarray
>>> ba = bitarray.bitarray()

Conversion from strings requires a bit of ceremony. Once upon a time, you could just use fromstring , but that method is now deprecated, since it has to implicitly encode the string into bytes. To avoid the inevitable encoding errors, it's better to pass a bytes object to frombytes . When starting from a string, that means you have to specify an encoding explicitly -- which is good practice anyway.

>>> ba.frombytes('Hi'.encode('utf-8'))
>>> ba
bitarray('0100100001101001')

Conversion to a list is easy. (Also, bitstring objects have a lot of list-like functions already.)

>>> l = ba.tolist()
>>> l
[False, True, False, False, True, False, False, False, 
 False, True, True, False, True, False, False, True]

bitstring s can be created from any iterable:

>>> bitarray.bitarray(l)
bitarray('0100100001101001')

Conversion back to bytes or strings is relatively easy too:

>>> bitarray.bitarray(l).tobytes().decode('utf-8')
'Hi'

And for the sake of sheer entertainment:

>>> def s_to_bitlist(s):
...     ords = (ord(c) for c in s)
...     shifts = (7, 6, 5, 4, 3, 2, 1, 0)
...     return [(o >> shift) & 1 for o in ords for shift in shifts]
... 
>>> def bitlist_to_chars(bl):
...     bi = iter(bl)
...     bytes = zip(*(bi,) * 8)
...     shifts = (7, 6, 5, 4, 3, 2, 1, 0)
...     for byte in bytes:
...         yield chr(sum(bit << s for bit, s in zip(byte, shifts)))
... 
>>> def bitlist_to_s(bl):
...     return ''.join(bitlist_to_chars(bl))
... 
>>> s_to_bitlist('Hi')
[0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 1]
>>> bitlist_to_s(s_to_bitlist('Hi'))
'Hi'

Answer 2

There are probably faster ways to do this, but using no extra modules:

def tobits(s):
    result = []
    for c in s:
        bits = bin(ord(c))[2:]
        bits = '00000000'[len(bits):] + bits
        result.extend([int(b) for b in bits])
    return result

def frombits(bits):
    chars = []
    for b in range(len(bits) / 8):
        byte = bits[b*8:(b+1)*8]
        chars.append(chr(int(''.join([str(bit) for bit in byte]), 2)))
    return ''.join(chars)

Answer 3

not sure why, but here are two ugly oneliners using only builtins:

s = "Hi"
l = map(int, ''.join([bin(ord(i)).lstrip('0b').rjust(8,'0') for i in s]))
s = "".join(chr(int("".join(map(str,l[i:i+8])),2)) for i in range(0,len(l),8))

yields:

>>> l
[0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 1]
>>> s
'Hi'

In real world code, use the struct or the bitarray module.

Answer 4

def text_to_bits(text):
    """
    >>> text_to_bits("Hi")
    [0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 1]
    """
    bits = bin(int.from_bytes(text.encode(), 'big'))[2:]
    return list(map(int, bits.zfill(8 * ((len(bits) + 7) // 8))))

def text_from_bits(bits):
    """
    >>> text_from_bits([0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 1])
    'Hi'
    """
    n = int(''.join(map(str, bits)), 2)
    return n.to_bytes((n.bit_length() + 7) // 8, 'big').decode()

See also, Convert Binary to ASCII and vice versa (Python) .

Answer 5

You could use the built-in bytearray :

>>> for i in bytearray('Hi', 'ascii'):
...     print(i)
... 
72
105

>>> bytearray([72, 105]).decode('ascii')
'Hi'

And bin() to convert to binary.

Answer 6

A few speed comparisons. Each of these were run using

python -m timeit "code"

or

cat <<-EOF | python -m timeit
    code
EOF

if multiline.

Bits to Byte

A : 100000000 loops, best of 3: 0.00838 usec per loop

res = 0
for idx,x in enumerate([0,0,1,0,1,0,0,1]):
    res |= (x << idx)

B : 100000000 loops, best of 3: 0.00838 usec per loop

int(''.join(map(str, [0,0,1,0,1,0,0,1])), 2)

Byte to Bits

A : 100000000 loops, best of 3: 0.00836 usec per loop

[(41 >> x) & 1 for x in range(7, -1, -1)]

B : 100000 loops, best of 3: 2.07 usec per loop

map(int, bin(41)[2:])

Answer 7

def to_bin(string):
    res = ''
    for char in string:
        tmp = bin(ord(char))[2:]
        tmp = '%08d' %int(tmp)
        res += tmp
    return res

def to_str(string):
    res = ''
    for idx in range(len(string)/8):
        tmp = chr(int(string[idx*8:(idx+1)*8], 2))
        res += tmp
    return res

These function is really simple.
It doesn't use third party module.

Answer 8

import math

class BitList:
    def __init__(self, value):
        if isinstance(value, str):
            value = sum([bytearray(value, "utf-8")[-i - 1] << (8*i) for i in range(len(bytearray(value, "utf-8")))])
        try:
            self.value = sum([value[-i - 1] << i for i in range(len(value))])
        except Exception:
            self.value = value

    def __getitem__(self, index):
        if isinstance(index, slice):
            if index.step != None and index.step != 1:
                return list(self)[index]
            else:
                start = index.start if index.start else 0
                stop = index.stop if index.stop != None else len(self)

                return BitList(math.floor((self.value % (2 ** (len(self) - start))) >> (len(self) - stop)))
        else:
            return bool(self[index:index + 1].value)

    def __len__(self):
        return math.ceil(math.log2(self.value + 1))

    def __str__(self):
        return self.value

    def __repr__(self):
        return "BitList(" + str(self.value) + ")"

    def __iter__(self):
        yield from [self[i] for i in range(len(self))]

Then you can initialize BitList with a number or a list (of numbers or booleans), then you can get its value, get positional items, get slices, and convert it to a list. Note: Cannot currently set items, but when I add that I will edit this post.

I made this my self, then went looking for how to convert a string (or a file) into a list of bits, then figured that out from another answer.

Answer 9

This might work, but it does not work if you ask PEP 8 (long line, complex)

tobits = lambda x: "".join(map(lambda y:'00000000'[len(bin(ord(y))[2:]):]+bin(ord(y))[2:],x))
frombits = lambda x: ''.join([chr(int(str(y), 2)) for y in [x[y:y+8] for y in range(0,len(x),8)]])

These are used like normal functions.

Answer 10

Because I like generators, I'll post my version here:

def bits(s):
    for c in s:
        yield from (int(bit) for bit in bin(ord(c))[2:].zfill(8))


def from_bits(b):
    for i in range(0, len(b), 8): 
        yield chr(int(''.join(str(bit) for bit in b[i:i + 8]), 2)) 


print(list(bits('Hi')))
[0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 1]
print(''.join(from_bits([0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 1])))
Hi

Answer 11

If you have bits in a list then you simply convert it into str and then to a number. Number will behave like a bit string and then bitwise operation can be applied. For example :

int(str([1,0,0,1]) | int(str([1,0,1,1])