The target architecture word size. One of :class:`Target.Bits`.

def bits(self):
        """
        The target architecture word size. One of :class:`Target.Bits`.
        """
        if self._bits is None:
            value = self._DEFAULT_BITS.get(self.arch)
            if value is None:
                raise NotImplementedError('Could not determine the default word size of %s architecture.' % self.arch)
            return value
        else:
            return self._bits