Defer starting the SAS session until needed

pyomo/solvers/plugins/solvers/SAS.py

@@ -195,7 +195,9 @@ def _presolve(self, *args, **kwds):
 
     def available(self, exception_flag=False):
         """True if the solver is available"""
-        return self._python_api_exists
+        if not self._python_api_exists:
+            return False
+        return self.start_sas_session() is not None
 
     def _has_integer_variables(self):
         """True if the problem has integer variables."""
@@ -285,12 +287,7 @@ def __init__(self, **kwds):
 
         # Store other options for the SAS session
         self._session_options = kwds
-
-        # Create the session
-        try:
-            self._sas_session = self._sas.SASsession(**self._session_options)
-        except:
-            self._sas_session = None
+        self._sas_session = None
 
     def __del__(self):
         # Close the session, if we created one
@@ -314,6 +311,15 @@ def _create_statement_str(self, statement):
     def sas_version(self):
         return self._sasver
 
+    def start_sas_session(self):
+        if self._sas_session is None:
+            # Create (and cache) the session
+            try:
+                self._sas_session = self._sas.SASsession(**self._session_options)
+            except:
+                pass
+        return self._sas_session
+
     def _apply_solver(self):
         """ "Prepare the options and run the solver. Then store the data to be returned."""
         logger.debug("Running SAS")
@@ -374,10 +380,7 @@ def _apply_solver(self):
         sas_options = "option notes nonumber nodate nosource pagesize=max;"
 
         # Get the current SAS session, submit the code and return the results
-        if not self._sas_session:
-            sas = self._sas_session = self._sas.SASsession(**self._session_options)
-        else:
-            sas = self._sas_session
+        sas = self.start_sas_session()
 
         # Find the version of 9.4 we are using
         self._sasver = sas.sasver
@@ -585,19 +588,23 @@ def __init__(self, **kwds):
             self._python_api_exists = True
 
         self._session_options = kwds
-
-        # Create the session
-        try:
-            self._sas_session = self._sas.CAS(**self._session_options)
-        except:
-            self._sas_session = None
+        self._sas_session = None
 
     def __del__(self):
         # Close the session, if we created one
         if self._sas_session:
             self._sas_session.close()
             del self._sas_session
 
+    def start_sas_session(self):
+        if self._sas_session is None:
+            # Create (and cache) the session
+            try:
+                self._sas_session = self._sas.CAS(**self._session_options)
+            except:
+                pass
+        return self._sas_session
+
     def _uploadMpsFile(self, s, unique):
         # Declare a unique table name for the mps table
         mpsdata_table_name = "mps" + unique

pyomo/solvers/tests/checks/test_SAS.py

@@ -26,7 +26,7 @@
     Suffix,
 )
 from pyomo.opt.results import SolverStatus, TerminationCondition, ProblemSense
-from pyomo.opt import SolverFactory, check_available_solvers
+from pyomo.opt import SolverFactory
 import warnings
 
 CFGFILE = os.environ.get("SAS_CFG_FILE_PATH", None)
@@ -38,7 +38,10 @@
 }
 
 
-sas_available = check_available_solvers("sas")
+try:
+    sas94_available = SolverFactory('_sas94').available()
+except:
+    sas94_available = False
 
 
 class SASTestAbc:
@@ -292,7 +295,7 @@ def test_solver_with_milp(self):
         )
 
 
-@unittest.skipIf(not sas_available, "The SAS solver is not available")
+@unittest.skipIf(not sas94_available, "The SAS94 solver interface is not available")
 class SASTestLP94(SASTestLP, unittest.TestCase):
     @mock.patch(
         "pyomo.solvers.plugins.solvers.SAS.SAS94.sas_version",
@@ -325,7 +328,7 @@ def test_solver_error(self, submit_mock, symget_mock):
         self.assertEqual(results.solver.status, SolverStatus.error)
 
 
-# @unittest.skipIf(not sas_available, "The SAS solver is not available")
+# @unittest.skipIf(not sascas_available, "The SAS solver is not available")
 @unittest.skip("Tests not yet configured for SAS Viya interface.")
 class SASTestLPCAS(SASTestLP, unittest.TestCase):
     solver_io = "_sascas"
@@ -526,13 +529,13 @@ def test_solver_warmstart_capable(self):
         self.assertTrue(self.opt_sas.warm_start_capable())
 
 
-# @unittest.skipIf(not sas_available, "The SAS solver is not available")
+# @unittest.skipIf(not sas94_available, "The SAS solver is not available")
 @unittest.skip("MILP94 tests disabled.")
 class SASTestMILP94(SASTestMILP, unittest.TestCase):
     pass
 
 
-# @unittest.skipIf(not sas_available, "The SAS solver is not available")
+# @unittest.skipIf(not sascas_available, "The SAS solver is not available")
 @unittest.skip("Tests not yet configured for SAS Viya interface.")
 class SASTestMILPCAS(SASTestMILP, unittest.TestCase):
     solver_io = "_sascas"