You can now add and edit context dependent units including dimensional exponents

src/ifcopenshell-python/ifcopenshell/api/unit/add_context_dependent_unit.py

@@ -0,0 +1,14 @@
+class Usecase:
+    def __init__(self, file, **settings):
+        self.file = file
+        self.settings = {"unit_type": "USERDEFINED", "name": "THINGAMAJIG", "dimensions": (0, 0, 0, 0, 0, 0, 0)}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        return self.file.create_entity(
+            "IfcContextDependentUnit",
+            Dimensions=self.file.createIfcDimensionalExponents(*self.settings["dimensions"]),
+            UnitType=self.settings["unit_type"],
+            Name=self.settings["name"],
+        )

src/ifcopenshell-python/ifcopenshell/api/unit/edit_named_unit.py

@@ -7,4 +7,12 @@ class Usecase:
 
     def execute(self):
         for name, value in self.settings["attributes"].items():
+            if name == "Dimensions":
+                dimensions = self.settings["unit"].Dimensions
+                if len(self.file.get_inverse(dimensions)) > 1:
+                    self.settings["unit"].Dimensions = self.file.createIfcDimensionalExponents(*value)
+                else:
+                    for i, exponent in enumerate(value):
+                        dimensions[i] = exponent
+                continue
             setattr(self.settings["unit"], name, value)

src/ifcopenshell-python/ifcopenshell/api/unit/remove_unit.py

@@ -1,3 +1,4 @@
+import ifcopenshell.util.unit
 import ifcopenshell.util.element
 
 
@@ -9,10 +10,12 @@ class Usecase():
             self.settings[key] = value
 
     def execute(self):
-        unit_assignment = self.file.by_type("IfcUnitAssignment")[0]
-        units = list(unit_assignment.Units)
-        units.remove(self.settings["unit"])
-        if not units:
-            return
-        unit_assignment.Units = units
+        unit_assignment = ifcopenshell.util.unit.get_unit_assignment(self.file)
+        if unit_assignment and self.settings["unit"] in unit_assignment.Units:
+            units = list(unit_assignment.Units)
+            units.remove(self.settings["unit"])
+            if units:
+                unit_assignment.Units = units
+            else:
+                self.file.remove(unit_assignment)
         ifcopenshell.util.element.remove_deep(self.file, self.settings["unit"])