Add types to remaining InternalSolver methods

miplearn/solvers/gurobi.py

@@ -17,6 +17,7 @@ from miplearn.solvers.internal import (
     LazyCallback,
     MIPSolveStats,
 )
+from miplearn.types import VarIndex
 
 logger = logging.getLogger(__name__)
 
@@ -230,7 +231,7 @@ class GurobiSolver(InternalSolver):
         else:
             return "max"
 
-    def get_value(self, var_name, index):
+    def get_value(self, var_name: str, index: VarIndex) -> Optional[float]:
         var = self._all_vars[var_name][index]
         return self._get_value(var)
 
@@ -244,26 +245,29 @@ class GurobiSolver(InternalSolver):
         else:
             return c.pi
 
-    def _get_value(self, var):
+    def _get_value(self, var: Any) -> Optional[float]:
         if self.cb_where == self.GRB.Callback.MIPSOL:
             return self.model.cbGetSolution(var)
         elif self.cb_where == self.GRB.Callback.MIPNODE:
             return self.model.cbGetNodeRel(var)
         elif self.cb_where is None:
-            return var.x
+            if self.is_infeasible():
+                return None
+            else:
+                return var.x
         else:
             raise Exception(
                 "get_value cannot be called from cb_where=%s" % self.cb_where
             )
 
-    def get_variables(self):
+    def get_empty_solution(self) -> Dict:
         self._raise_if_callback()
-        variables = {}
+        solution: Dict = {}
         for (varname, vardict) in self._all_vars.items():
-            variables[varname] = []
+            solution[varname] = {}
             for (idx, var) in vardict.items():
-                variables[varname] += [idx]
-        return variables
+                solution[varname][idx] = None
+        return solution
 
     def add_constraint(self, constraint, name=""):
         if type(constraint) is tuple:
@@ -325,7 +329,7 @@ class GurobiSolver(InternalSolver):
         else:
             raise Exception("Unknown sense: %s" % sense)
 
-    def get_inequality_slacks(self):
+    def get_inequality_slacks(self) -> Dict[str, float]:
         ineqs = [c for c in self.model.getConstrs() if c.sense != "="]
         return {c.ConstrName: c.Slack for c in ineqs}
 
@@ -341,7 +345,7 @@ class GurobiSolver(InternalSolver):
         c = self.model.getConstrByName(cid)
         c.RHS = rhs
 
-    def relax(self):
+    def relax(self) -> None:
         self.model = self.model.relax()
         self._update_vars()