python module pass basic test

src/data.h

@@ -242,7 +242,7 @@ class FMatrixS : public FMatrixInterface<FMatrixS>{
    * \brief save column access data into stream
    * \param fo output stream to save to
    */
-  inline void SaveColAccess(utils::IStream &fo) {
+  inline void SaveColAccess(utils::IStream &fo) const {
     fo.Write(&num_buffered_row_, sizeof(num_buffered_row_));
     if (num_buffered_row_ != 0) {
       SaveBinary(fo, col_ptr_, col_data_);

src/io/io.cpp

@@ -15,7 +15,12 @@ DataMatrix* LoadDataMatrix(const char *fname, bool silent, bool savebuffer) {
 }
 
 void SaveDataMatrix(const DataMatrix &dmat, const char *fname, bool silent) {
-  utils::Error("not implemented");
+  if (dmat.magic == DMatrixSimple::kMagic){
+    const DMatrixSimple *p_dmat = static_cast<const DMatrixSimple*>(&dmat);
+    p_dmat->SaveBinary(fname, silent);
+  } else {
+    utils::Error("not implemented");
+  }
 }
 
 }  // namespace io

src/io/simple_dmatrix-inl.hpp

@@ -148,7 +148,7 @@ class DMatrixSimple : public DataMatrix {
    * \param fname name of binary data
    * \param silent whether print information or not
    */
-  inline void SaveBinary(const char* fname, bool silent = false) {
+  inline void SaveBinary(const char* fname, bool silent = false) const {
     utils::FileStream fs(utils::FopenCheck(fname, "wb"));
     int magic = kMagic;
     fs.Write(&magic, sizeof(magic));

src/learner/dmatrix.h

@@ -58,7 +58,7 @@ struct MetaInfo {
       return 0;
     }
   }
-  inline void SaveBinary(utils::IStream &fo) {
+  inline void SaveBinary(utils::IStream &fo) const {
     fo.Write(&num_row, sizeof(num_row));
     fo.Write(&num_col, sizeof(num_col));
     fo.Write(labels);