code: def iter_zeros(self):
          
          num = quotient = 0
          while num < self._len:
              chunk = self.data[quotient]
              if chunk & self.zero_mask:
                  remainder = 0
                  while remainder < self.width and num < self._len:
                      item = (chunk >> remainder) & 3
                      if item == PC_ZERO:
                          yield num
                      remainder += 2
                      num += 1
              else:
                  num += (self.width >> 1)
              quotient += 1
docs: Iterate through the indices of all zero items.