code: def _init(self, width, len_):
          
          self._width = width
          self._len = len_
          bits = len_ * width
          self._data = bytearray(BinInt(bits).ceildiv(8))
docs: Initializes internal data representation of the BinArray to all-0.
          The internal data representation is simply tightly-packed bits of all
          words, starting from LSB, split into bytes and stored in a bytearray.
          The unused trailing padding bits in the last byte must always be set
          to 0.