BUG: fix unit comparison for K VS degC

docs/usage.rst

@@ -363,9 +363,9 @@ Performing arithmetic with temperature quantities can be ambiguous. To clarify i
   >>> t1 = 23*degC
   >>> t2 = 1*delta_degC
   >>> print(t1 + t2)
-  24 °C
+  24.0 °C
   >>> print(t2 - t1)
-  -22 °C
+  -22.0 °C
   >>> tempco = 10.0*V/delta_degC
   >>> print(tempco*2*delta_degC)
   20.0 V

unyt/array.py

@@ -1884,7 +1884,11 @@ def __array_ufunc__(self, ufunc, method, *inputs, **kwargs):
                     conv, offset = u1.get_conversion_factor(u0, inp1.dtype)
                     new_dtype = np.dtype("f" + str(inp1.dtype.itemsize))
                     conv = new_dtype.type(conv)
-                    if offset is not None:
+                    if (
+                        offset is not None
+                        and u1.base_offset != 0.0
+                        and not repr(u0).startswith("delta_")
+                    ):
                         raise InvalidUnitOperation(
                             "Quantities with units of Fahrenheit or Celsius "
                             "cannot by multiplied, divided, subtracted or "

unyt/tests/test_units.py

@@ -504,15 +504,25 @@ def test_base_equivalent():
     assert u.get_base_equivalent(unit_system="mks") == Unit("A")
 
 
-def test_temperature_offsets():
-    u1 = Unit("degC")
-    u2 = Unit("degF")
-
+@pytest.mark.parametrize(
+    ("u1", "u2"),
+    [
+        (Unit("degC"), Unit("degF")),
+        (Unit("degC"), Unit("K")),
+        (Unit("degF"), Unit("K")),
+    ],
+)
+def test_temperature_offsets(u1, u2):
     with pytest.raises(InvalidUnitOperation):
         operator.mul(u1, u2)
     with pytest.raises(InvalidUnitOperation):
         operator.truediv(u1, u2)
 
+    assert u1 != u2
+    assert u2 != u1
+    assert not u1 == u2
+    assert not u2 == u1
+
 
 def test_latex_repr():
     registry = UnitRegistry()

unyt/unit_object.py

@@ -480,25 +480,18 @@ def __pow__(self, p):
 
     def __eq__(self, u):
         """Test unit equality."""
-        if not isinstance(u, Unit):
-            return False
         return (
-            math.isclose(self.base_value, u.base_value)
-            and self.dimensions == u.dimensions
+            isinstance(u, Unit)
+            and math.isclose(self.base_value, u.base_value)
+            and math.isclose(self.base_offset, u.base_offset)
+            and (
+                # use 'is' comparison dimensions to avoid expensive sympy operation
+                self.dimensions is u.dimensions
+                # fall back to expensive sympy comparison
+                or self.dimensions == u.dimensions
+            )
         )
 
-    def __ne__(self, u):
-        """Test unit inequality."""
-        if not isinstance(u, Unit):
-            return True
-        if not math.isclose(self.base_value, u.base_value):
-            return True
-        # use 'is' comparison dimensions to avoid expensive sympy operation
-        if self.dimensions is u.dimensions:
-            return False
-        # fall back to expensive sympy comparison
-        return self.dimensions != u.dimensions
-
     def copy(self, *, deep=False):
         expr = str(self.expr)
         base_value = copy.deepcopy(self.base_value)