def METHOD_NAME(self, axis=None):
    """Returns the number of stored values, including explicit zeros.
    Args:
        axis: Not supported yet.
    Returns:
        int: The number of stored values.
    """
    if axis is not None:
        raise NotImplementedError(
            'getnnz over an axis is not implemented for DIA format')
    m, n = self.shape
    nnz = _core.ReductionKernel(
        'int32 offsets, int32 m, int32 n', 'int32 nnz',
        'offsets > 0 ? min(m, n - offsets) : min(m + offsets, n)',
        'a + b', 'nnz = a', '0', 'dia_nnz')(self.offsets, m, n)
    return int(nnz)