[ReactorNet] improve handling of max_time_step

* implement ReactorNet::maxTimeStep to allow for external queries
* implement getter/setter for property ReactorNet.max_time_step
* deprecate ReactorNet.set_max_time_step

include/cantera/zeroD/ReactorNet.h

@@ -35,6 +35,11 @@ public:
     //! using the current mixture state as the initial condition.
     void setInitialTime(double time);
 
+    //! Get the maximum time step.
+    double maxTimeStep() {
+        return m_maxstep;
+    }
+
     //! Set the maximum time step.
     void setMaxTimeStep(double maxstep);
 

interfaces/cython/cantera/_cantera.pxd

@@ -630,6 +630,7 @@ cdef extern from "cantera/zerodim.h" namespace "Cantera":
         void setTolerances(double, double)
         double rtol()
         double atol()
+        double maxTimeStep()
         void setMaxTimeStep(double)
         void setMaxErrTestFails(int)
         void setMaxSteps(int)

interfaces/cython/cantera/reactor.pyx

@@ -887,7 +887,7 @@ cdef class Valve(FlowDevice):
              Renamed to `set_pressure_function`.
         """
         warnings.warn("To be removed after Cantera 2.5. "
-                      "Renamed to `set_pressure_function` instead", DeprecationWarning)
+                      "Renamed to 'set_pressure_function' instead", DeprecationWarning)
 
         self.set_pressure_function(k)
 
@@ -909,8 +909,8 @@ cdef class Valve(FlowDevice):
              `set_pressure_function`.
         """
         warnings.warn("To be removed after Cantera 2.5. "
-                      "Use property `valve_coeff` and/or function "
+                      "Use property 'valve_coeff' and/or function "
-                      "`set_pressure_function` instead.", DeprecationWarning)
+                      "'set_pressure_function' instead.", DeprecationWarning)
 
         if isinstance(k, _numbers.Real):
             self.valve_coeff = k
@@ -972,7 +972,7 @@ cdef class PressureController(FlowDevice):
              Replaced by property `pressure_coeff`.
         """
         warnings.warn("To be removed after Cantera 2.5. "
-                      "Use property `pressure_coeff` instead", DeprecationWarning)
+                      "Use property 'pressure_coeff' instead", DeprecationWarning)
         (<CxxPressureController*>self.dev).setPressureCoeff(k)
 
     def set_master(self, FlowDevice d):
@@ -1052,11 +1052,30 @@ cdef class ReactorNet:
         """
         self.net.setInitialTime(t)
 
+    property max_time_step:
+        """
+        Get/set the maximum time step *t* [s] that the integrator is
+        allowed to use. The default value is set to zero, i.e. no time
+        step maximum is used.
+        """
+        def __get__(self):
+            return self.net.maxTimeStep()
+
+        def __set__(self, double t):
+            self.net.setMaxTimeStep(t)
+
     def set_max_time_step(self, double t):
         """
         Set the maximum time step *t* [s] that the integrator is allowed
         to use.
+
+        .. deprecated:: 2.5
+
+             To be deprecated with version 2.5, and removed thereafter.
+             Replaced by property `max_time_step`.
         """
+        warnings.warn("To be removed after Cantera 2.5. "
+                      "Use property 'max_time_step' instead", DeprecationWarning)
         self.net.setMaxTimeStep(t)
 
     property max_err_test_fails:

interfaces/cython/cantera/test/test_reactor.py

@@ -149,7 +149,20 @@ class TestReactor(utilities.CanteraTest):
         tEnd = 10.0
         dt_max = 0.07
         t = tStart
-        self.net.set_max_time_step(dt_max)
+
+        with warnings.catch_warnings(record=True) as w:
+
+            # cause all warnings to always be triggered.
+            warnings.simplefilter("always")
+            self.net.set_max_time_step(dt_max)
+
+            self.assertEqual(len(w), 1)
+            self.assertTrue(issubclass(w[-1].category, DeprecationWarning))
+            self.assertIn("To be removed after Cantera 2.5. ",
+                          str(w[-1].message))
+
+        self.net.max_time_step = dt_max
+        self.assertEqual(self.net.max_time_step, dt_max)
         self.net.set_initial_time(tStart)
         self.assertNear(self.net.time, tStart)
 
@@ -169,7 +182,7 @@ class TestReactor(utilities.CanteraTest):
         max_steps = 10
         max_step_size = 1e-07
         self.net.set_initial_time(0)
-        self.net.set_max_time_step(max_step_size)
+        self.net.max_time_step = max_step_size
         self.net.max_steps = max_steps
         with self.assertRaisesRegex(
                 ct.CanteraError, 'mxstep steps taken before reaching tout'):
@@ -461,7 +474,7 @@ class TestReactor(utilities.CanteraTest):
         self.assertNear(mfc.mdot(1.2), 0.)
 
         self.net.rtol = 1e-11
-        self.net.set_max_time_step(0.05)
+        self.net.max_time_step = 0.05
         self.net.advance(2.5)
 
         mb = self.r1.volume * self.r1.density
@@ -900,7 +913,7 @@ class TestWellStirredReactorIgnition(utilities.CanteraTest):
 
     def test_ignition3(self):
         self.setup(900.0, 10*ct.one_atm, 1.0, 80.0)
-        self.net.set_max_time_step(0.5)
+        self.net.max_time_step = 0.5
         t,T = self.integrate(100.0)
         self.assertTrue(T[-1] < 910) # mixture did not ignite
 
@@ -978,8 +991,8 @@ class TestConstPressureReactor(utilities.CanteraTest):
 
         self.net1 = ct.ReactorNet([self.r1])
         self.net2 = ct.ReactorNet([self.r2])
-        self.net1.set_max_time_step(0.05)
+        self.net1.max_time_step = 0.05
-        self.net2.set_max_time_step(0.05)
+        self.net2.max_time_step = 0.05
         self.net2.max_err_test_fails = 10
 
     def test_component_index(self):