Ensure value of expressions is Python int (#517)

* add tests for dtype

* fix objective value in OR-Tools

* fix objective value in Gurobi

* ensure result of wsum is int

* fix __pow__

cpmpy/expressions/core.py

@@ -329,10 +329,11 @@ def __rmod__(self, other):
 
     def __pow__(self, other, modulo=None):
         assert (modulo is None), "Power operator: modulo not supported"
-        if other == 0:
-            return 1
-        elif other == 1:
-            return self
+        if is_num(other):
+            if other == 0:
+                return 1
+            if other == 1:
+                return self
         return Operator("pow", [self, other])
 
     def __rpow__(self, other, modulo=None):
@@ -541,7 +542,7 @@ def value(self):
         if any(a is None for a in arg_vals): return None
         # non-boolean
         elif self.name == "sum": return sum(arg_vals)
-        elif self.name == "wsum": return sum(arg_vals[0]*np.array(arg_vals[1]))
+        elif self.name == "wsum": return int(sum(arg_vals[0]*np.array(arg_vals[1])))
         elif self.name == "mul": return arg_vals[0] * arg_vals[1]
         elif self.name == "sub": return arg_vals[0] - arg_vals[1]
         elif self.name == "mod": return arg_vals[0] % arg_vals[1]

cpmpy/solvers/gurobi.py

@@ -180,7 +180,11 @@ def solve(self, time_limit=None, solution_callback=None, **kwargs):
                     cpm_var._value = int(solver_val)
             # set _objective_value
             if self.has_objective():
-                self.objective_value_ = grb_objective.getValue()
+                grb_obj_val = grb_objective.getValue()
+                if grb_obj_val != int(grb_obj_val):
+                    self.objective_value_ =  grb_obj_val # can happen with DirectVar using floats
+                else:
+                    self.objective_value_ = int(grb_obj_val)
 
         return has_sol
 

cpmpy/solvers/ortools.py

@@ -217,7 +217,9 @@ def solve(self, time_limit=None, assumptions=None, solution_callback=None, **kwa
 
             # translate objective
             if self.has_objective():
-                self.objective_value_ = self.ort_solver.ObjectiveValue()
+                ort_obj_val = self.ort_solver.ObjectiveValue()
+                assert int(ort_obj_val) == ort_obj_val, "Objective value should be integer, please report on github"
+                self.objective_value_ = int(ort_obj_val) # ensure it is an integer
 
         return has_sol
 

tests/test_expressions.py

@@ -531,6 +531,35 @@ def test_description(self):
         self.assertEqual(str(cons), "either a or b should be true, but not both -- (a) or (b)")
 
 
+    def test_dtype(self):
+
+        x = cp.intvar(1,10,shape=(3,3), name="x")
+        self.assertTrue(cp.Model(cp.sum(x) >= 10).solve())
+        self.assertIsNotNone(x.value())
+        print(x.value())
+        # test all types of expressions
+        self.assertEqual(int, type(x[0,0].value())) # just the var
+        for v in x[0]:
+            self.assertEqual(int, type(v.value())) # array of var
+        self.assertEqual(int, type(cp.sum(x[0]).value()))
+        self.assertEqual(int, type(cp.sum(x).value()))
+        self.assertEqual(int, type(cp.sum([1,2,3] * x[0]).value()))
+        self.assertEqual(int, type(cp.sum(np.array([1, 2, 3]) * x[0]).value()))
+        a,b = x[0,[0,1]]
+        self.assertEqual(int, type((-a).value()))
+        self.assertEqual(int, type((a - b).value()))
+        self.assertEqual(int, type((a * b).value()))
+        self.assertEqual(int, type((a // b).value()))
+        self.assertEqual(int, type((a ** b).value()))
+        self.assertEqual(int, type((a % b).value()))
+
+
+
+
+
+
+
+
 class TestBuildIns(unittest.TestCase):
 
     def setUp(self):