How to pack arbitrary bit sequence in Python?

Question

I want to encode/compress some binary image data as a sequence if bits. (This sequence will, in general, have a length that does not fit neatly in a whole number of standar

Answer 1

There's nothing very convenient built in but there are third-party modules such as bitstring and bitarray which are designed for this.

from bitstring import BitArray
s = BitArray('0b11011')
s += '0b100'
s += 'uint:5=9'
s += [0, 1, 1, 0, 1]
...
s.tobytes()

To join together a sequence of 3-bit numbers (i.e. range 0->7) you could use

>>> symbols = [0, 4, 5, 3, 1, 1, 7, 6, 5, 2, 6, 2]
>>> BitArray().join(BitArray(uint=x, length=3) for x in symbols)
BitArray('0x12b27eab2')
>>> _.tobytes()
'\x12\xb2~\xab '

Some related questions:

• What is the best way to do Bit Field manipulation in Python?
• Python Bitstream implementations