In my application I need to pack bits of a specified group size into integral values. Currently np.packbits only packs into full bytes. For example, I might have a string of bits encoded as a np.uint8 vector with each uint8 item specifying a single bit 1/0. I want to encode them 4 bits at a time into a np.uint32 vector. python code to implement this: --------------- def pack_bits (inp, bits_per_word, dir=1, dtype=np.int32): assert bits_per_word <= np.dtype(dtype).itemsize * 8 assert len(inp) % bits_per_word == 0 out = np.empty (len (inp)//bits_per_word, dtype=dtype) i = 0 o = 0 while i < len(inp): ret = 0 for b in range (bits_per_word): if dir > 0: ret |= inp[i] << b else: ret |= inp[i] << (bits_per_word - b - 1) i += 1 out[o] = ret o += 1 return out --------------- It looks like unpackbits has a "count" parameter but packbits does not. Also would be good to be able to specify an output dtype.