Support converting from aliased to alias units

src/property_utils/tests/units/test_converter_types.py

@@ -26,8 +26,10 @@
     Unit3,
     Unit4,
     Unit5,
+    Unit6,
     Unit1Converter,
     UnregisteredConverter,
+    Unit1_2Converter,
     Unit1_314Converter,
     Unit2_4Converter,
     Unit3_2Converter,
@@ -38,6 +40,7 @@
     Unit1Unit4FractionConverter,
     Unit1_2Unit4_3Converter,
     Unit5Converter,
+    Unit6Converter,
 )
 
 
@@ -377,6 +380,28 @@ def test_from_B_to_b(self):
         self.assertResultRaises(UnsupportedConverterError)
 
 
+@add_to(ExponentiatedUnitConverter_test_suite)
+class TestAliasExponentiatedUnitConverterConvert(TestCase):
+    def subject(self, value, from_descriptor, to_descriptor):
+        return Unit1_2Converter.convert(value, from_descriptor, to_descriptor)
+
+    @args({"value": 2, "from_descriptor": Unit1.A**2, "to_descriptor": Unit1.A**2})
+    def test_with_same_unit(self):
+        self.assertResult(2)
+
+    @args({"value": 5, "from_descriptor": Unit1.A**2, "to_descriptor": Unit1.a**2})
+    def test_with_same_unit_type(self):
+        self.assertResult(500)
+
+    @args({"value": 5, "from_descriptor": Unit1.A**2, "to_descriptor": Unit6.F})
+    def test_with_alias_units(self):
+        self.assertResult(250)
+
+    @args({"value": 10, "from_descriptor": Unit1.a**2, "to_descriptor": Unit6.f})
+    def test_with_alias_si_units(self):
+        self.assertResult(10)
+
+
 @add_to(ExponentiatedUnitConverter_test_suite)
 class TestExponentiatedUnitConverterGetFactor(TestCase):
     def subject(self, from_descriptor, to_descriptor):

src/property_utils/units/converter_types.py

@@ -495,7 +495,12 @@ def get_factor(
                 f"invalid 'to_descriptor'; expected an instance of {cls.generic_unit_descriptor}. "
             )
         from_dimension = Dimension.from_descriptor(from_descriptor)
+
+        if isinstance(to_descriptor, AliasMeasurementUnit):
+            return cls._get_aliased_factor(from_dimension, to_descriptor)
+
         to_dimension = Dimension.from_descriptor(to_descriptor)
+
         try:
             converter = get_converter(cls.generic_unit_descriptor.unit_type)
         except UndefinedConverterError:
@@ -514,6 +519,35 @@ def get_factor(
         factor = converter.get_factor(from_dimension.unit, to_dimension.unit)
         return factor**to_dimension.power
 
+    @classmethod
+    def _get_aliased_factor(
+        cls, from_dimension: Dimension, to_descriptor: AliasMeasurementUnit
+    ) -> float:
+        """
+        Returns the conversion factor from an alias unit to its aliased.
+
+        The conversion happens in four steps:
+
+        1. Convert from the alias unit to the SI unit.
+        2. Convert from the SI unit to the aliased SI units (this step is not
+        implemented in code, because the conversion factor is 1)
+        3. Convert from the aliased SI units to the target units.
+
+        e.g. if you want to convert from cm^3 to L:
+        1. cm^3 -> m^3
+        2. m^3 -> kL (conversion factor 1)
+        3. kL -> L
+        """
+        step_1_factor = cls.get_factor(from_dimension, from_dimension.si())
+
+        converter = get_converter(to_descriptor.to_generic())
+
+        step_3_factor = converter.convert(
+            1, to_descriptor.to_generic().to_si(), to_descriptor
+        )
+
+        return step_1_factor * step_3_factor
+
 
 class CompositeUnitConverter(metaclass=ABCMeta):
     """