Python interface for SPEX

 SPEX Left LU is a software package designed to exactly solve unsymmetric sparse
 linear systems, Ax = b, where A, b and x contain rational numbers. This
 package performs a left-looking, roundoff-error-free (REF) LU factorization
 PAQ = LDU, where L and U are integer, D is diagonal, and P and Q are row and
 column permutations, respectively. Note that the matrix D is never explicitly
 computed nor needed; thus this package uses only the matrices L and U.