[Cython] Added interface to Reactor.component_index

interfaces/cython/cantera/_cantera.pxd

@@ -17,6 +17,7 @@ cdef extern from "cantera/base/ctml.h" namespace "ctml":
 
 cdef extern from "cantera/base/global.h" namespace "Cantera":
     cdef void CxxAddDirectory "Cantera::addDirectory" (string)
+    cdef size_t CxxNpos "Cantera::npos"
 
 cdef extern from "cantera/thermo/mix_defs.h":
     cdef int thermo_type_ideal_gas "Cantera::cIdealGas"
@@ -253,6 +254,7 @@ cdef extern from "cantera/zeroD/Reactor.h":
         void setKineticsMgr(CxxKinetics&)
         void setEnergy(int)
         cbool energyEnabled()
+        size_t componentIndex(string&)
 
         void addSensitivityReaction(size_t) except +
         size_t nSensParams()

interfaces/cython/cantera/reactor.pyx

@@ -196,6 +196,20 @@ cdef class Reactor(ReactorBase):
     def add_sensitivity_reaction(self, m):
         self.reactor.addSensitivityReaction(m)
 
+    def component_index(self, name):
+        """
+        Returns the index of the component named *name* in the system. This
+        determines the (relative) index of the component in the vector of
+        sensitivity coefficients. *name* is either a species name or the name
+        of a reactor state variable, e.g. 'U', 'T', depending on the reactor's
+        equations.
+        """
+
+        k = self.reactor.componentIndex(stringify(name))
+        if k == CxxNpos:
+            raise IndexError('No such component: {!r}'.format(name))
+        return k
+
 
 cdef class Reservoir(ReactorBase):
     """

interfaces/cython/cantera/test/test_reactor.py

@@ -58,6 +58,14 @@ class TestReactor(utilities.CanteraTest):
         self.r1.name = 'hello'
         self.assertEqual(self.r1.name, 'hello')
 
+    def test_component_index(self):
+        self.make_reactors(n_reactors=1)
+        self.net.step(1.0)
+
+        N0 = self.net.n_vars - self.gas1.n_species
+        for i, name in enumerate(self.gas1.species_names):
+            self.assertEqual(i + N0, self.r1.component_index(name))
+
     def test_disjoint(self):
         T1, P1 = 300, 101325
         T2, P2 = 500, 300000