[Units] Add Cython interface for some functions

include/cantera/base/Units.h

@@ -62,7 +62,7 @@ class Units
     bool operator==(const Units& other) const;
 
     //! Return dimension of primary unit component
-    //! ("mass", "length", "time", "temperature", "current" or "quantity")
+    //! ("mass", "length", "time", "temperature", "current", or "quantity")
     double dimension(const std::string& primary) const;
 
 private:

interfaces/cython/cantera/_cantera.pxd

@@ -100,6 +100,7 @@ cdef extern from "cantera/base/Units.h" namespace "Cantera":
         CxxUnits(string, cbool) except +translate_exception
         string str()
         double factor()
+        double dimension(string) except +translate_exception
 
     cdef cppclass CxxUnitSystem "Cantera::UnitSystem":
         CxxUnitSystem()

interfaces/cython/cantera/composite.py

@@ -670,7 +670,7 @@ def ndim(self) -> int:
     def shape(self) -> tuple[int, ...]:
         """The shape of the SolutionArray.
 
-        .. versionadded: 3.0
+        .. versionadded:: 3.0
 
         :return: A tuple of integers with the number of elements in each dimension.
         """
@@ -680,7 +680,7 @@ def shape(self) -> tuple[int, ...]:
     def size(self) -> int:
         """The number of elements in the SolutionArray.
 
-        .. versionadded: 3.0
+        .. versionadded:: 3.0
         """
         return np.prod(self.shape)
 

interfaces/cython/cantera/thermo.pyx

@@ -732,10 +732,10 @@ cdef class ThermoPhase(_SolutionBase):
         :param basis:
             Determines if ``fuel`` and ``oxidizer`` are given in mole
             fractions (``basis='mole'``) or mass fractions (``basis='mass'``)
-        :param: diluent:
+        :param diluent:
             Optional parameter. Required if dilution is used. Specifies the composition
             of the diluent in mole/mass fractions as a string, array or dict
-        :param: fraction:
+        :param fraction:
             Optional parameter. Dilutes the fuel/oxidizer mixture with the diluent
             according to ``fraction``. Fraction can refer to the fraction of diluent in
             the  mixture (for example ``fraction="diluent:0.7`` will create a mixture

interfaces/cython/cantera/units.pyx

@@ -1,5 +1,6 @@
 # This file is part of Cantera. See License.txt in the top-level directory or
 # at https://cantera.org/license.txt for license and copyright information.
+from typing import Dict
 
 cdef class Units:
     """
@@ -18,8 +19,40 @@ cdef class Units:
         if name:
             self.units = CxxUnits(stringify(name), True)
 
-    def __repr__(self):
-        return f"<Units({pystr(self.units.str())}) at {id(self):0x}>"
+    def __repr__(self) -> str:
+        return f"<Units({str(self)}) at {id(self):0x}>"
+
+    def __str__(self) -> str:
+        return pystr(self.units.str())
+
+    def dimension(self, primary: str) -> float:
+        """The dimension of the given unit component.
+
+        .. versionadded:: 3.0
+
+        :param primary:
+            A string with the desired unit component. One of ``"mass"``,
+            ``"length"``, ``"time"``, ``"temperature"``, ``"current"``, or
+            ``"quantity"``.
+        """
+        return self.units.dimension(stringify(primary))
+
+    @property
+    def dimensions(self) -> Dict[str, str]:
+        """A dictionary of the primary unit components to their dimensions.
+
+        .. versionadded:: 3.0
+        """
+        dimensions = ("mass", "length", "time", "temperature", "current", "quantity")
+        return {d: self.dimension(d) for d in dimensions}
+
+    @property
+    def factor(self) -> float:
+        """The factor required to convert from this unit to Cantera's base units.
+
+        .. versionadded:: 3.0
+        """
+        return self.units.factor()
 
     @staticmethod
     cdef copy(CxxUnits other):