Convert Bytes To Bits in Python

Converting bytes to bits in Python involves representing each byte in its binary form, where each byte is composed of 8 bits. For example , a byte like 0xAB (which is 171 in decimal) would be represented as '10101011' in binary. Let’s explore a few techniques to convert bytes to bits in Python.

Using int.from_bytes(...).bit_length()

This method converts a byte sequence to an integer using int.from_bytes() and then calculates the number of bits required to represent that integer using .bit_length().

a = b'\x01\x23\x45\x67\x89\xAB\xCD\xEF'

b = int.from_bytes(a, byteorder='big').bit_length()
print(b) 

57

Explanation: int.from_bytes(a, byteorder='big').bit_length() converts a byte sequence a to an integer (big-endian) and returns the number of bits needed to represent that integer.

Using generator expression

This method counts the number of 1 bits in each byte of the byte sequence by converting each byte to its binary form and counting the occurrences of 1 using a generator expression and bin(byte).count('1').

a = b'\x01\x23\x45\x67\x89\xAB\xCD\xEF'
b = sum(bin(byte).count('1') for byte in a)
print(b) 

32

Explanation: sum(bin(byte).count('1') for byte in a) converts each byte in a to binary, counts the number of 1 bits and sums them up.

Using bitwise shift

This approach constructs the integer by shifting each byte into its correct position using bitwise left shift (<<) and OR (|). After constructing the full integer, it calculates the bit length using .bit_length().

a = b'\x01\x23\x45\x67\x89\xAB\xCD\xEF'
val = 0

for byte in a:
    val = (val << 8) | byte
b = val.bit_length()
print(b)

57

Explanation: for byte in a: val = (val << 8) | byte constructs an integer val by shifting it left by 8 bits for each byte and OR'ing the byte. After all bytes are processed, val.bit_length() returns the number of bits needed to represent val.

Using binary string join

This method creates a binary string by converting each byte to its 8-bit binary representation and joining them. Then, it calculates the bit length by measuring the length of the binary string after stripping leading zeros.

a = b'\x01\x23\x45\x67\x89\xAB\xCD\xEF'
binary_str = ''.join(f"{byte:08b}" for byte in a)
b = len(binary_str.lstrip('0'))
print(b)

57

Explanation: ''.join(f"{byte:08b}" for byte in a) converts each byte in a to its 8-bit binary form and concatenates them into one string. binary_str.lstrip('0') removes leading zeros and len(binary_str) calculates the number of remaining bits.