Add writeBasis interface method to highspy

highspy/highs_bindings.cpp

@@ -735,6 +735,7 @@ PYBIND11_MODULE(highs_bindings, m)
     .def("passRowName", &Highs::passRowName)
     .def("readModel", &Highs::readModel)
     .def("readBasis", &Highs::readBasis)
+    .def("writeBasis", &Highs::writeBasis)
     .def("presolve", &Highs::presolve)
     .def("run", &Highs::run)
     .def("postsolve", &Highs::postsolve)

highspy/tests/test_highspy.py

@@ -1,3 +1,4 @@
+import tempfile
 import unittest
 import highspy
 import numpy as np
@@ -404,3 +405,37 @@ def test_ranging(self):
         self.assertEqual(ranging.row_bound_up.value_[1], inf);
         self.assertEqual(ranging.row_bound_up.objective_[1], inf);
 
+    def test_write_basis_before_running(self):
+        h = self.get_basic_model()
+        with tempfile.NamedTemporaryFile() as f:
+            h.writeBasis(f.name)
+            contents = f.read()
+            self.assertEqual(contents, b'HiGHS v1\nNone\n')
+
+    def test_write_basis_after_running(self):
+        h = self.get_basic_model()
+        h.run()
+        with tempfile.NamedTemporaryFile() as f:
+            h.writeBasis(f.name)
+            contents = f.read()
+            self.assertEqual(
+                contents, b'HiGHS v1\nValid\n# Columns 2\n1 1 \n# Rows 2\n0 0 \n'
+            )
+
+    def test_read_basis(self):
+        # Read basis from one run model into an unrun model
+        expected_status_before = highspy.HighsBasisStatus.kLower
+        expected_status_after = highspy.HighsBasisStatus.kBasic
+
+        h1 = self.get_basic_model()
+        self.assertEqual(h1.getBasis().col_status[0], expected_status_before)
+        h1.run()
+        self.assertEqual(h1.getBasis().col_status[0], expected_status_after)
+
+        h2 = self.get_basic_model()
+        self.assertEqual(h2.getBasis().col_status[0], expected_status_before)
+
+        with tempfile.NamedTemporaryFile() as f:
+            h1.writeBasis(f.name)
+            h2.readBasis(f.name)
+            self.assertEqual(h2.getBasis().col_status[0], expected_status_after)