def clear(self):
        """Convenience method to reset all the block values to 0
        """
        if self._bit_count == 0:
            return

        block = self._qpart.document().begin()
        while block.isValid():
            if self.getBlockValue(block):
                self.setBlockValue(block, 0)
            block = block.next()
Convenience method to reset all the block values to 0