'Returns a column-sorted list of non-zero elements of the matrix.
Examples
>>> from sympy.matrices import SparseMatrix
>>> a=SparseMatrix(((1, 2), (3, 4)))
>>> a
Matrix([
[1, 2],
[3, 4]])
>>> a.CL
[(0, 0, 1), (1, 0, 3), (0, 1, 2), (1, 1, 4)]
See Also
col_op
row_list'

def col_list(self):

    return [tuple((k + (self[k],))) for k in sorted(list(self._smat.keys()), key=(lambda k: list(reversed(k))))]
