[Reactor] Check for Reactor contents before installing FlowDevice

Fixes #279.

interfaces/cython/cantera/_cantera.pxd

@@ -518,7 +518,7 @@ cdef extern from "cantera/zeroD/flowControllers.h":
     cdef cppclass CxxFlowDevice "Cantera::FlowDevice":
         CxxFlowDevice()
         double massFlowRate(double) except +
-        cbool install(CxxReactorBase&, CxxReactorBase&)
+        cbool install(CxxReactorBase&, CxxReactorBase&) except +
         void setFunction(CxxFunc1*)
         void setParameters(int, double*)
 

interfaces/cython/cantera/test/test_reactor.py

@@ -434,6 +434,19 @@ class TestReactor(utilities.CanteraTest):
             self.assertNear(speciesMass(kAr), mAr)
             self.assertNear(speciesMass(kO2), mO2)
 
+    def test_valve_errors(self):
+        self.make_reactors()
+        res = ct.Reservoir()
+
+        with self.assertRaises(RuntimeError):
+            # Must assign contents of both reactors before creating Valve
+            v = ct.Valve(self.r1, res)
+
+        v = ct.Valve(self.r1, self.r2)
+        with self.assertRaises(RuntimeError):
+            # inlet and outlet cannot be reassigned
+            v._install(self.r2, self.r1)
+
     def test_pressure_controller(self):
         self.make_reactors(n_reactors=1)
         g = ct.Solution('h2o2.xml')

src/zeroD/FlowDevice.cpp

@@ -9,7 +9,7 @@ namespace Cantera
 bool FlowDevice::install(ReactorBase& in, ReactorBase& out)
 {
     if (m_in || m_out) {
-        return false;
+        throw CanteraError("FlowDevice::install", "Already installed");
     }
     m_in =  ∈
     m_out = &out;
@@ -20,7 +20,8 @@ bool FlowDevice::install(ReactorBase& in, ReactorBase& out)
     ThermoPhase* mixin = &m_in->contents();
     ThermoPhase* mixout = &m_out->contents();
     if (mixin == 0 || mixout == 0) {
-        return false;
+        throw CanteraError("FlowDevice::install", "Can't install flow device "
+            "until reactor contents have been assigned.");
     }
 
     m_nspin = mixin->nSpecies();