[Python] Outline of a strategy for wrapping classes which extend Transport

interfaces/cython/cantera/_cantera.pxd

@@ -61,7 +61,6 @@ cdef extern from "cantera/transport/DustyGasTransport.h" namespace "Cantera":
     cdef cppclass CxxDustyGasTransport "Cantera::DustyGasTransport":
         void setPorosity(double) except +
 
-
 cdef extern from "cantera/equil/MultiPhase.h" namespace "Cantera":
     cdef cppclass CxxMultiPhase "Cantera::MultiPhase":
         CxxMultiPhase()

interfaces/cython/cantera/base.pyx

@@ -30,11 +30,12 @@ cdef class _SolutionBase:
         else:
             self.kinetics = NULL
 
-        # Transport
+        # Initialization of transport is deferred to Transport.__init__
+        self.transport = NULL
+
+    def __init__(self, *args, **kwargs):
         if isinstance(self, Transport):
-            self.transport = newDefaultTransportMgr(self.thermo)
-        else:
-            self.transport = NULL
+            assert self.transport is not NULL
 
     def __dealloc__(self):
         del self.thermo

interfaces/cython/cantera/composite.pyx

@@ -1,6 +1,8 @@
 class Solution(ThermoPhase, Kinetics, Transport):
-    def __init__(self, *args, **kwars):
-        pass
+    pass
 
 class Interface(InterfacePhase, Kinetics):
     pass
+
+class DustyGas(ThermoPhase, Kinetics, DustyGasTransport):
+    pass

interfaces/cython/cantera/test/test_transport.py

@@ -9,3 +9,9 @@ class TestTransport(utilities.CanteraTest):
 
     def test_viscosity(self):
         self.assertTrue(self.phase.viscosity > 0.0)
+
+class TestDustyGas(utilities.CanteraTest):
+    def test_methods(self):
+        self.phase = ct.DustyGas('h2o2.xml')
+
+        self.phase.setPorosity(0.2)

interfaces/cython/cantera/transport.pyx

@@ -1,4 +1,17 @@
 cdef class Transport(_SolutionBase):
+    def __init__(self, *args, **kwargs):
+        if self.transport == NULL:
+            self.transport = newDefaultTransportMgr(self.thermo)
+        super().__init__(*args, **kwargs)
+
     property viscosity:
         def __get__(self):
             return self.transport.viscosity()
+
+cdef class DustyGasTransport(Transport):
+    def __init__(self, *args, **kwargs):
+        self.transport = newTransportMgr(stringify("DustyGas"), self.thermo)
+        super().__init__(*args, **kwargs)
+
+    def setPorosity(self, value):
+        (<CxxDustyGasTransport*>self.transport).setPorosity(value)