[Cython/Thermo] Add mass/mole_fraction_dict methods

This complements the ability to set the composition using a dict when working
with phases with different sets of species.

interfaces/cython/cantera/_cantera.pxd

@@ -86,6 +86,7 @@ cdef extern from "cantera/thermo/ThermoPhase.h" namespace "Cantera":
         void setMassFractionsByName(string) except +
         void setMassFractionsByName(stdmap[string,double]&) except +
         void setMassFractions_NoNorm(double*) except +
+        stdmap[string,double] getMassFractionsByName(double)
         double massFraction(size_t) except +
         double massFraction(string) except +
 
@@ -93,6 +94,7 @@ cdef extern from "cantera/thermo/ThermoPhase.h" namespace "Cantera":
         void setMoleFractionsByName(stdmap[string,double]&) except +
         void setMoleFractions_NoNorm(double*) except +
         void getMoleFractions(double*) except +
+        stdmap[string,double] getMoleFractionsByName(double)
         double moleFraction(size_t) except +
         double moleFraction(string) except +
 

interfaces/cython/cantera/_cantera.pyx

@@ -5,7 +5,7 @@ import numpy as np
 cimport numpy as np
 import math
 
-from cython.operator cimport dereference as deref
+from cython.operator cimport dereference as deref, preincrement as inc
 
 from _cantera cimport *
 

interfaces/cython/cantera/test/test_thermo.py

@@ -94,6 +94,16 @@ class TestThermoPhase(utilities.CanteraTest):
         self.assertNear(Y[0], 0.25)
         self.assertNear(Y[3], 0.75)
 
+    def test_getCompositionDict(self):
+        self.phase.X = 'OH:1e-9, O2:0.4, AR:0.6'
+        self.assertEqual(len(self.phase.mole_fraction_dict(1e-7)), 2)
+        self.assertEqual(len(self.phase.mole_fraction_dict()), 3)
+
+        self.phase.Y = 'O2:0.4, AR:0.6'
+        Y1 = self.phase.mass_fraction_dict()
+        self.assertNear(Y1['O2'], 0.4)
+        self.assertNear(Y1['AR'], 0.6)
+
     def test_setCompositionNoNorm(self):
         X = np.zeros(self.phase.n_species)
         X[2] = 1.0

interfaces/cython/cantera/thermo.pyx

@@ -344,6 +344,14 @@ cdef class ThermoPhase(_SolutionBase):
             raise ValueError("Array has incorrect length")
         self.thermo.setMoleFractions_NoNorm(&data[0])
 
+    def mass_fraction_dict(self, double threshold=0.0):
+        Y = self.thermo.getMassFractionsByName(threshold)
+        return {pystr(item.first):item.second for item in Y}
+
+    def mole_fraction_dict(self, double threshold=0.0):
+        X = self.thermo.getMoleFractionsByName(threshold)
+        return {pystr(item.first):item.second for item in X}
+
     ######## Read-only thermodynamic properties ########
 
     property P: