Merge pull request #3716 from rschwarz/rs/3589-gurobi-direct-logtoconsole

Set LogToConsole instead of OutputFlag to handle "tee"

Author: mrmundt

pyomo/solvers/plugins/solvers/gurobi_direct.py

@@ -239,10 +239,13 @@ def available(self, exception_flag=True):
     def _apply_solver(self):
         StaleFlagManager.mark_all_as_stale()
 
-        if self._tee:
-            self._solver_model.setParam('OutputFlag', 1)
-        else:
-            self._solver_model.setParam('OutputFlag', 0)
+        # We would like to just set OutputFlag to turn off the console
+        # log, but that prevents users from using the Gurobi LogFile
+        # option (see #3589 / #3716).  BUT just setting LogToConsole
+        # triggers Gurobi to write a message to the console.  We will
+        # capture that message here:
+        with capture_output(capture_fd=True):
+            self._solver_model.setParam('LogToConsole', int(bool(self._tee)))
 
         if self._keepfiles:
             # Only save log file when the user wants to keep it.

pyomo/solvers/tests/checks/test_gurobi_direct.py

@@ -134,9 +134,9 @@ def setParam(self, param, value):
                 opt.solve(self.model, options={"MIPFocus": 2})
 
         # Method should not be set again, but MIPFocus was changed.
-        # OutputFlag is explicitly set on the model.
+        # LogToConsole is explicitly set on the model.
         assert envparams == {"Method": 2, "MIPFocus": 1}
-        assert modelparams == {"MIPFocus": 2, "OutputFlag": 0}
+        assert modelparams == {"MIPFocus": 2, "LogToConsole": 0}
 
     # Try an erroneous parameter setting to ensure parameters go through in all
     # cases. Expect an error to indicate pyomo tried to set the parameter.