LearningSolver: accept any callable function as solver

src/python/miplearn/solvers.py

@@ -2,13 +2,16 @@
 #  Copyright (C) 2020, UChicago Argonne, LLC. All rights reserved.
 #  Released under the modified BSD license. See COPYING.md for more details.
 
-from . import ObjectiveValueComponent, PrimalSolutionComponent, LazyConstraintsComponent
+import logging
+from copy import deepcopy
+
 import pyomo.environ as pe
+from p_tqdm import p_map
 from pyomo.core import Var
-from copy import deepcopy
 from scipy.stats import randint
-from p_tqdm import p_map
-import logging
+
+from . import ObjectiveValueComponent, PrimalSolutionComponent, LazyConstraintsComponent
+
 logger = logging.getLogger(__name__)
 
 
@@ -274,8 +277,9 @@ class LearningSolver:
             solver = CPLEXSolver()
         elif self.internal_solver_factory == "gurobi":
             solver = GurobiSolver()
-        elif issubclass(self.internal_solver_factory, InternalSolver):
+        elif callable(self.internal_solver_factory):
             solver = self.internal_solver_factory()
+            assert isinstance(solver, InternalSolver)
         else:
             raise Exception("solver %s not supported" % self.internal_solver_factory)
         solver.set_threads(self.threads)

src/python/miplearn/tests/test_solver.py

@@ -4,7 +4,7 @@
 
 from miplearn import LearningSolver, BranchPriorityComponent
 from miplearn.problems.knapsack import KnapsackInstance
-import pickle, tempfile
+from miplearn.solvers import GurobiSolver
 
 
 def _get_instance():
@@ -18,7 +18,7 @@ def _get_instance():
 def test_solver():
     instance = _get_instance()
     for mode in ["exact", "heuristic"]:
-        for internal_solver in ["cplex", "gurobi"]:
+        for internal_solver in ["cplex", "gurobi", GurobiSolver]:
             solver = LearningSolver(time_limit=300,
                                     gap_tolerance=1e-3,
                                     threads=1,