[Python] Add Quantity.set_equivalence_ratio and set_mixture_fraction

Fixes #1446

interfaces/cython/cantera/composite.py

@@ -302,6 +302,20 @@ def equilibrate(self, XY=None, *args, **kwargs):
         self.phase.equilibrate(XY, *args, **kwargs)
         self.state = self._phase.state
 
+    def set_equivalence_ratio(self, phi, fuel, oxidizer, basis="mole", *, diluent=None,
+                              fraction=None):
+        self._phase.state = self.state
+        self._phase.set_equivalence_ratio(phi, fuel, oxidizer, basis, diluent=diluent,
+                                          fraction=fraction)
+        self.state = self._phase.state
+    set_equivalence_ratio.__doc__ = Solution.set_equivalence_ratio.__doc__
+
+    def set_mixture_fraction(self, mixture_fraction, fuel, oxidizer, basis='mole'):
+        self._phase.state = self.state
+        self._phase.set_mixture_fraction(mixture_fraction, fuel, oxidizer, basis)
+        self.state = self._phase.state
+    set_mixture_fraction.__doc__ = Solution.set_mixture_fraction.__doc__
+
     def __imul__(self, other):
         self.mass *= other
         return self

test/python/test_thermo.py

@@ -1639,6 +1639,23 @@ def test_extensive(self):
         self.assertNear(q1.entropy, q1.S)
         self.assertNear(q1.gibbs, q1.G)
 
+    def test_set_equivalence_ratio(self):
+        q1 = ct.Quantity(self.gas, mass=3)
+        T1, P1 = q1.TP
+        q1.set_equivalence_ratio(2.0, 'CH4:1.0', 'O2:1.0, N2:3.76')
+        assert q1.T == approx(T1)
+        assert q1.P == approx(P1)
+        assert q1.X[q1.species_index('CH4')] == approx(1.0 / (1 + 4.76))
+
+    def test_set_mixture_fraction(self):
+        q1 = ct.Quantity(self.gas, mass=3)
+        T1, P1 = q1.TP
+        q1.set_mixture_fraction(1.0, 'CH3OH:1.0', 'O2:1.0, N2:3.76')
+        assert q1.T == approx(T1)
+        assert q1.P == approx(P1)
+        assert q1.mass == 3
+        assert q1.X[q1.species_index('CH3OH')] == approx(1.0)
+
     def test_basis(self):
         q1 = ct.Quantity(self.gas, mass=5)
         T1, P1 = q1.TP