Allows addition and substraction between different property classes w…

…ith same units

src/property_utils/properties/property.py

@@ -316,10 +316,10 @@ def __add__(self, other) -> Self:
             >>> x1 + x2
             <Property: 20 m>
         """
-        if not isinstance(other, self.__class__):
+        if not isinstance(other, Property):
             raise PropertyBinaryOperationError(
-                f"cannot add {other} to ({self}); {other} is not a {self.__class__}; "
-                "only same properties can be added to each other. "
+                f"cannot add {other} to ({self}); {other} is not a Property; "
+                "only properties can be added to properties. "
             )
         if not self.unit.isinstance_equivalent(other.unit.to_generic()):
             raise PropertyBinaryOperationError(
@@ -364,11 +364,10 @@ def __sub__(self, other) -> Self:
             >>> t1 - t2
             <Property: 1.0 min>
         """
-        if not isinstance(other, self.__class__):
+        if not isinstance(other, Property):
             raise PropertyBinaryOperationError(
                 f"cannot subtract {other} from ({self}); {other} is not a "
-                f"{self.__class__}; only same properties can be subtracted from each "
-                "other. "
+                "Property; only properties can be subtracted from properties. "
             )
         if not self.unit.isinstance_equivalent(other.unit.to_generic()):
             raise PropertyBinaryOperationError(
@@ -389,7 +388,7 @@ def __sub__(self, other) -> Self:
             ) from None
         return self.__class__(self.value - prop.value, self.unit)
 
-    def __rsub__(self, other) -> Self:
+    def __rsub__(self, other) -> "Property":
         """
         Defines right subtraction between properties.
 
@@ -400,7 +399,7 @@ def __rsub__(self, other) -> Self:
             >>> t1 - t2
             <Property: 1.0 min>
         """
-        if not isinstance(other, self.__class__):
+        if not isinstance(other, Property):
             raise PropertyBinaryOperationError(
                 f"cannot subtract {self} from ({other}); {other} is not a "
                 f"{self.__class__}; only same properties can be subtracted from each "

src/property_utils/tests/properties/test_property.py

@@ -743,6 +743,20 @@ def test_with_other_aliased_units(self):
         self.assert_result("25.0 H")
 
 
+@add_to(property_test_suite)
+class TestDifferentPropertyAddition(TestProperty):
+    def subject(self, left, right):
+        return left + right
+
+    @args({"left": PropUnit1(10), "right": Property(10, Unit1.a)})
+    def test_left_operand(self):
+        self.assert_result("20 a")
+
+    @args({"left": Property(10, Unit1.a), "right": PropUnit1(10)})
+    def test_right_operand(self):
+        self.assert_result("20 a")
+
+
 @add_to(property_test_suite, "__sub__")
 class TestSimplePropertySubtraction(TestProperty):
 
@@ -834,6 +848,16 @@ def test_with_other_aliased_units(self):
         self.assert_result("15.0 H")
 
 
+@add_to(property_test_suite)
+class TestDifferentPropertySubtraction(TestProperty):
+    def subject(self, prop):
+        return PropUnit1(10) - prop
+
+    @args({"prop": Property(5, Unit1.a)})
+    def test_with_base_property_class(self):
+        self.assert_result("5 a")
+
+
 @add_to(property_test_suite, "__rsub__")
 class TestSimplePropertyRightSubtraction(TestProperty):
 
@@ -883,6 +907,16 @@ def test_with_other_aliased_si_units(self):
         self.assert_result("-60.0 f / (d^2)")
 
 
+@add_to(property_test_suite)
+class TestDifferentPropertyRightSubtraction(TestProperty):
+    def subject(self, prop):
+        return prop - PropUnit1(5)
+
+    @args({"prop": Property(10, Unit1.a)})
+    def test_with_base_property_class(self):
+        self.assert_result("5 a")
+
+
 @add_to(property_test_suite, "__pow__")
 class TestPropertyExponentiation(TestProperty):