Simplify composite non dimensionals

src/property_utils/tests/api/test_api.py

@@ -42,3 +42,19 @@ def test_sub(self):
     @args({"p1": p(11, JOULE / KELVIN), "p2": p(10, JOULE / KELVIN), "op": ge})
     def test_greater_or_equal(self):
         self.assertResultTrue()
+
+    @args({"p1": p(1) ** 2, "p2": p(1), "op": add})
+    def test_non_dimensionals_addition(self):
+        self.assert_result("2.0 ")
+
+    @args({"p1": p(1) / p(1), "p2": p(1), "op": add})
+    def test_non_dimensionals_addition_2(self):
+        self.assert_result("2.0 ")
+
+    @args({"p1": p(1) / (p(1) ** 2), "p2": p(1), "op": add})
+    def test_non_dimensionals_addition_3(self):
+        self.assert_result("2.0 ")
+
+    @args({"p1": (p(1) ** 2) ** 3, "p2": p(1), "op": add})
+    def test_non_dimensionals_addition_4(self):
+        self.assert_result("2.0 ")

src/property_utils/tests/data.py

@@ -115,6 +115,14 @@ def si(cls) -> "Unit8":
         return cls.h
 
 
+class Unit9(MeasurementUnit):
+    NON_DIMENSIONAL = ""
+
+    @classmethod
+    def is_non_dimensional(cls) -> bool:
+        return True
+
+
 class UnregisteredConverter(AbsoluteUnitConverter): ...
 
 
@@ -262,6 +270,10 @@ def dimension_7(power: float = 1) -> Dimension:
     return Dimension(Unit7.G, power)
 
 
+def dimension_9(power: float = 1) -> Dimension:
+    return Dimension(Unit9.NON_DIMENSIONAL, power)
+
+
 def generic_dimension_1(power: float = 1) -> GenericDimension:
     """
     Unit1^power

src/property_utils/tests/units/test_descriptors.py

@@ -29,13 +29,15 @@
     Unit5,
     Unit6,
     Unit7,
+    Unit9,
     dimension_1,
     dimension_2,
     dimension_3,
     dimension_4,
     dimension_5,
     dimension_6,
     dimension_7,
+    dimension_9,
     generic_dimension_1,
     generic_dimension_2,
     generic_dimension_3,
@@ -68,14 +70,12 @@
 
 @add_to(MeasurementUnitMeta_test_suite)
 class TestMeasurementUnitMetaInverseGeneric(TestDescriptor):
-
     def test_inverse_generic(self):
         self.assertSequenceEqual(str(Unit1.inverse_generic()), " / Unit1", str)
 
 
 @add_to(MeasurementUnitMeta_test_suite)
 class TestMeasurementUnitMetaMultiplication(TestDescriptorBinaryOperation):
-
     operator = mul
     produced_type = GenericCompositeDimension
 
@@ -116,7 +116,6 @@ def test_with_int(self):
 
 @add_to(MeasurementUnitMeta_test_suite)
 class TestMeasurementUnitMetaDivision(TestDescriptorBinaryOperation):
-
     operator = truediv
     produced_type = GenericCompositeDimension
 
@@ -227,7 +226,6 @@ def test_with_generic_composite_dimension_same_numerator(self):
 
 @add_to(MeasurementUnit_test_suite)
 class TestMeasurementUnitFromDescriptor(TestDescriptor):
-
     def subject(self, descriptor):
         return MeasurementUnit.from_descriptor(descriptor)
 
@@ -266,7 +264,6 @@ def test_with_generic_composite_dimension(self):
 
 @add_to(MeasurementUnit_test_suite)
 class TestMeasurementUnitIsInstance(TestDescriptor):
-
     def subject(self, generic):
         return Unit1.A.isinstance(generic)
 
@@ -301,7 +298,6 @@ def test_with_generic_composite_dimension(self):
 
 @add_to(MeasurementUnit_test_suite)
 class TestMeasurementUnitIsInstanceEquivalent(TestDescriptor):
-
     def subject(self, descriptor):
         return Unit3.C.isinstance_equivalent(descriptor)
 
@@ -472,6 +468,22 @@ def test_with_none(self):
         self.assertResultRaises(DescriptorExponentError)
 
 
+@add_to(MeasurementUnit_test_suite)
+class TestNonDimensionalMeasurementUnitExponentiation(TestDescriptor):
+    produced_type = Dimension
+
+    def subject(self, value):
+        return Unit9.NON_DIMENSIONAL**value
+
+    @args({"value": 2})
+    def test_with_positive_int(self):
+        self.assert_result("")
+
+    @args({"value": -10})
+    def test_with_negative_int(self):
+        self.assert_result("")
+
+
 @add_to(AliasMeasurementUnit_test_suite)
 class TestAliasMeasurementUnitFromDescriptor(TestDescriptor):
     def subject(self, descriptor):
@@ -1378,6 +1390,19 @@ def subject(self, value):
         return dimension_1() ** value
 
 
+@add_to(Dimension_test_suite)
+class TestNonDimensionalDimensionExponentiation(
+    TestNonDimensionalMeasurementUnitExponentiation
+):
+    """
+    Repeat all tests in `TestNonDimensionalMeasurementUnitExponentiation` but with
+    dimension_9() as descriptor.
+    """
+
+    def subject(self, value):
+        return dimension_9() ** value
+
+
 @add_to(Dimension_test_suite)
 class TestExponentiatedDimensionExponentiation(TestDescriptor):
     produced_type = Dimension
@@ -2006,6 +2031,7 @@ def test_with_aliased_denominator_composite_dimension(self):
     def test_with_fully_aliased_composite_dimension(self):
         self.assertResultTrue()
 
+
 @add_to(GenericCompositeDimension_test_suite)
 class TestGenericCompositeDimensionHasNoUnits(TestDescriptor):
     def test_with_measurement_units(self):
@@ -2547,6 +2573,14 @@ def test_same_denominator_dimensions(self):
     def test_same_numerator_dimensions_zero_sum(self):
         self.assert_result(" / C")
 
+    @args({"composite": CompositeDimension([dimension_9()], [dimension_9()])})
+    def test_non_dimensionals(self):
+        self.assert_result("")
+
+    @args({"composite": CompositeDimension([dimension_9(3)], [dimension_9()])})
+    def test_non_dimensionals_exponentiated(self):
+        self.assert_result("")
+
 
 @add_to(CompositeDimension_test_suite)
 class TestCompositeDimensionSimplified(TestCompositeDimensionSimplify):
@@ -2576,6 +2610,7 @@ def test_objects_are_not_persisted(self):
         self.assertNotEqual(ids(composite.numerator), ids(inverse.denominator))
         self.assertNotEqual(ids(composite.denominator), ids(inverse.numerator))
 
+
 @add_to(CompositeDimension_test_suite)
 class TestCompositeDimensionHasNoUnits(TestDescriptor):
     def test_with_units(self):
@@ -2585,10 +2620,11 @@ def test_with_no_units(self):
         self.assertTrue(CompositeDimension().has_no_units())
 
     def test_with_same_unit_type(self):
-        self.assertFalse(CompositeDimension([Unit1.A],[Unit1.a]).has_no_units())
+        self.assertFalse(CompositeDimension([Unit1.A], [Unit1.a]).has_no_units())
 
     def test_with_same_unit(self):
-        self.assertFalse(CompositeDimension([Unit1.A],[Unit1.A]).has_no_units())
+        self.assertFalse(CompositeDimension([Unit1.A], [Unit1.A]).has_no_units())
+
 
 @add_to(CompositeDimension_test_suite)
 class TestCompositeDimensionMultiplication(TestDescriptorBinaryOperation):

src/property_utils/units/converters.py

@@ -13,6 +13,7 @@
 from property_utils.units.descriptors import UnitDescriptor
 from property_utils.exceptions.units.converter_types import UnitConversionError
 from property_utils.units.units import (
+    NonDimensionalUnit,
     RelativeTemperatureUnit,
     AbsoluteTemperatureUnit,
     LengthUnit,
@@ -94,9 +95,7 @@ def inverse(self) -> float:
 
 
 @register_converter(RelativeTemperatureUnit)
-class RelativeTemperatureUnitConverter(
-    RelativeUnitConverter
-):  # pylint: disable=too-few-public-methods
+class RelativeTemperatureUnitConverter(RelativeUnitConverter):  # pylint: disable=too-few-public-methods
     """
     Convert temperature units with this converter.
 
@@ -155,6 +154,17 @@ def convert(
         return value * cls.get_factor(from_descriptor, to_descriptor)
 
 
+@register_converter(NonDimensionalUnit)
+class NonDimensionalUnitConverter(AbsoluteUnitConverter):
+    """
+    This converter is needed for compatibility, i.e. for conversions to work from
+    non-dimensional units to non-dimensional dimensions.
+    """
+
+    reference_unit = NonDimensionalUnit.NON_DIMENSIONAL
+    conversion_map = {NonDimensionalUnit.NON_DIMENSIONAL: 1}
+
+
 @register_converter(LengthUnit)
 class LengthUnitConverter(AbsoluteUnitConverter):
     """

src/property_utils/units/descriptors.py

@@ -320,6 +320,22 @@ def si(cls) -> "MeasurementUnit":
         """
         raise NotImplementedError
 
+    @classmethod
+    def is_non_dimensional(cls) -> bool:
+        """
+        Implement this function for defined measurement units that are non dimensional.
+
+        Examples:
+            >>> class NonDimensionalUnit(MeasurementUnit):
+            ...     NON_DIMENSIONAL = ""
+            ...     @classmethod
+            ...     def is_non_dimensional(cls) -> bool: return True
+
+            >>> NonDimensionalUnit.is_non_dimensional()
+            True
+        """
+        return False
+
     @staticmethod
     def from_descriptor(descriptor: UnitDescriptor) -> "MeasurementUnit":
         """
@@ -468,6 +484,9 @@ def __pow__(self, power: float) -> "Dimension":
             >>> LengthUnit.FEET**3
             <Dimension: ft^3>
         """
+        # always keep non dimensional units to the first power
+        power = 1 if self.is_non_dimensional() else power
+
         return Dimension(self, power)
 
     def __hash__(self) -> int:
@@ -1009,7 +1028,10 @@ def __pow__(self, power: float) -> "Dimension":
                 f"invalid exponent: {{ value: {power}, type: {type(power)} }};"
                 " expected float or int. "
             )
-        self.power *= power
+        if self.unit.is_non_dimensional():
+            self.power = 1
+        else:
+            self.power *= power
         return self
 
     def __eq__(self, dimension) -> bool:
@@ -1701,6 +1723,9 @@ def simplify(self) -> None:
         numerator = []
         denominator = []
         for unit, exponent in exponents.items():
+            if unit.is_non_dimensional():
+                continue  # do not add non dimensional units to the simplified composite
+
             if exponent > 0:
                 numerator.append(Dimension(unit) ** exponent)
             elif exponent < 0:

src/property_utils/units/units.py

@@ -34,6 +34,10 @@ class NonDimensionalUnit(MeasurementUnit):
     def si(cls) -> "NonDimensionalUnit":
         return cls.NON_DIMENSIONAL
 
+    @classmethod
+    def is_non_dimensional(cls) -> bool:
+        return True
+
 
 class RelativeTemperatureUnit(MeasurementUnit):
     CELCIUS = "°C"