When creating variable-sized random binary strings with random.getrandbits(), you currently have to special case when the number of bytes is 0, because otherwise getrandbits() raises:

  ValueError: number of bits must be greater than zero

It seems like it wouldn't hurt to simply return 0 in that case.

The actual snippet looks something like:

  random.getrandombits(nbytes * 8).to_bytes(nbytes, 'little')