Similar to (right) null spaces, a left null space can be computed in Sage with the matrix method .left_kernel(). For a matrix $A$, elements of the (right) null space are vectors $\vect{x}$ such that $A\vect{x}=\zerovector$. If we interpret a vector placed to the left of a matrix as a 1-row matrix, then the product $\vect{x}A$ can be interpreted, according to our definition of matrix multiplication (Definition MM, as the entries of the vector $\vect{x}$ providing the scalars for a linear combination of the rows of the matrix $A$. So you can view each vector in the left null space naturally as the entries of a matrix with a single row, $Y$, with the property that $YA=\zeromatrix$.
Given Sage's preference for row vectors, the simpler name .kernel() is a synonym for .left_kernel(). Given your text's preference for column vectors, we will continue to rely on the .right_kernel(). Left kernels in Sage have the same options as right kernels and produce vector spaces as output in the same manner. Once created, a vector space all by itself (with no history) is neither left or right. Here is a quick repeat of Example LNS.