[Thermo] Adds getPhase function

getPhase returns the phase (liquid, vapor, etc.) of the phase. Not
implemented in the base ThermoPhase, must be overridden in derived
classes because it only makes sense for phases that can have multiple
phases.

include/cantera/thermo/PureFluidPhase.h

@@ -37,6 +37,20 @@ class PureFluidPhase : public ThermoPhase
         return "PureFluid";
     }
 
+    virtual std::string getPhase() const {
+        if (temperature() >= critTemperature() || pressure() >= critPressure()) {
+            return "supercritical";
+        } else if (m_sub->TwoPhase() == 1) {
+            return "twophase";
+        } else {
+            if (temperature() > satTemperature(pressure())) {
+                return "vapor";
+            } else {
+                return "liquid";
+            }
+        }
+    }
+
     //! Set the name of the TPX substance to use for the equation of state. This
     //! function should be called before initThermo().
     void setSubstance(const std::string& name) {

include/cantera/thermo/ThermoPhase.h

@@ -109,6 +109,11 @@ class ThermoPhase : public Phase
         return "ThermoPhase";
     }
 
+    //! String indicating the phase (liquid, vapor, etc.) of the phase
+    virtual std::string getPhase() const {
+        throw NotImplementedError("ThermoPhase::getPhase");
+    }
+
     /**
      * Returns the reference pressure in Pa. This function is a wrapper
      * that calls the species thermo refPressure function.

interfaces/cython/cantera/_cantera.pxd

@@ -126,6 +126,7 @@ cdef extern from "cantera/thermo/ThermoPhase.h" namespace "Cantera":
 
         # miscellaneous
         string type()
+        string getPhase()
         string report(cbool, double) except +translate_exception
         string name()
         void setName(string)

interfaces/cython/cantera/thermo.pyx

@@ -1631,6 +1631,13 @@ cdef class PureFluid(ThermoPhase):
         def __get__(self):
             return self.s, self.v, self.X
 
+    property phase:
+        """
+        Get the phase (vapor, liquid, etc.) at the current conditions.
+        """
+        def __get__(self):
+            return pystr(self.thermo.getPhase())
+
 
 class Element:
     """