Assembly.remove implementation (#1776)

* Initial Assembly.remove implementation

* Lint pass

* Added test for removing a name that does not exist and renamed the tests for clarity

* Probably got overzealous since a child should never be without a parent assembly

* Nevermind, mypy fails if the parent is not checked

* Added simple, top-down handling of constraint removal

* Took constraint removal back out

* Added a note to the docstring about the caveats of this new remove method

Author: jmwright

cadquery/assembly.py

@@ -232,6 +232,41 @@ def add(self, arg, **kwargs):
 
         return self
 
+    def remove(self, name: str) -> "Assembly":
+        """
+        Remove a part/subassembly from the current assembly.
+
+        :param name: Name of the part/subassembly to be removed
+        :return: The modified assembly
+
+        *NOTE* This method can cause problems with deeply nested assemblies and does not remove
+        constraints associated with the removed part/subassembly.
+        """
+
+        # Make sure the part/subassembly is actually part of the assembly
+        if name not in self.objects:
+            raise ValueError(f"No object with name '{name}' found in the assembly")
+
+        # Get the part/assembly to be removed
+        to_remove = self.objects[name]
+
+        # Remove the part/assembly from the parent's children list
+        if to_remove.parent:
+            to_remove.parent.children.remove(to_remove)
+
+        # Remove the part/assembly from the assembly's object dictionary
+        del self.objects[name]
+
+        # Remove all descendants from the objects dictionary
+        for descendant_name in to_remove._flatten().keys():
+            if descendant_name in self.objects:
+                del self.objects[descendant_name]
+
+        # Update the parent reference
+        to_remove.parent = None
+
+        return self
+
     def _query(self, q: str) -> Tuple[str, Optional[Shape]]:
         """
         Execute a selector query on the assembly.

tests/test_assembly.py

@@ -1705,3 +1705,101 @@ def test_step_export_filesize(tmpdir):
         filesize[i] = stepfile.stat().st_size
 
     assert filesize[1] < 1.2 * filesize[0]
+
+
+def test_assembly_remove_no_name_match():
+    """
+    Tests to make sure that removing a part/subassembly with a name that does not exist fails.
+    """
+
+    assy = cq.Assembly()
+    assy.add(box(1, 1, 1), name="part1")
+    assy.add(box(2, 2, 2), name="part2")
+
+    with pytest.raises(ValueError):
+        assy.remove("part3")
+
+
+def test_assembly_remove_part():
+    """
+    Tests the ability to remove a part from an assembly.
+    """
+    assy = cq.Assembly()
+    assy.add(box(1, 1, 1), name="part1")
+    assy.add(box(2, 2, 2), name="part2", loc=cq.Location(5.0, 5.0, 5.0))
+
+    # Make sure we have the correct number of children (2 parts)
+    assert len(assy.children) == 2
+    assert len(assy.objects) == 3
+
+    # Remove the first part
+    assy.remove("part1")
+
+    # Make sure we have the correct number of children (1 part)
+    assert len(assy.children) == 1
+    assert len(assy.objects) == 2
+
+
+def test_assembly_remove_subassy():
+    """
+    Tests the ability to remove a subassembly from an assembly.
+    """
+
+    # Create the top-level assembly
+    assy = cq.Assembly()
+    assy.add(box(1, 1, 1), name="loplevel_part1")
+
+    # Create the subassembly
+    subassy = cq.Assembly()
+    subassy.add(box(1, 1, 1), name="part1")
+    subassy.add(box(2, 2, 2), name="part2", loc=cq.Location(5.0, 5.0, 5.0))
+
+    # Add the subassembly to the top-level assembly
+    assy.add(subassy, name="subassy")
+
+    # Make sure we have the 1 top-level part and the subassembly
+    assert len(assy.children) == 2
+    assert len(assy.objects) == 5
+
+    # Remove the subassembly
+    assy.remove("subassy")
+
+    # Make sure we have the correct number of children (1 part)
+    assert len(assy.children) == 1
+    assert len(assy.objects) == 2
+
+    # Recreate the assembly with a nested subassembly
+    assy = cq.Assembly()
+    assy.add(box(1, 1, 1), name="loplevel_part1")
+    subassy = cq.Assembly()
+    subassy.add(box(1, 1, 1), name="part1")
+    subassy.add(box(2, 2, 2), name="part2", loc=cq.Location(2.0, 2.0, 2.0))
+    assy.add(subassy, name="subassy")
+
+    # Try to remove a part from a subassembly by using the path string
+    assert len(assy.children[1].children) == 2
+    assy.remove("subassy/part2")
+    assert len(assy.children[1].children) == 1
+
+
+def test_remove_without_parent():
+    """
+    Tests the ability to remove a part from an assembly when the part has no parent.
+    This may never happen in practice, but the case has to be covered for mypy to pass.
+    """
+
+    # Create a root assembly
+    assy = cq.Assembly(name="root")
+
+    # Create a part and add it to the assembly
+    part = cq.Workplane().box(1, 1, 1)
+    assy.add(part, name="part")
+
+    # Artificially remove the parent to cover a branching test case
+    assy.children[0].parent = None
+
+    # Remove the part
+    assy.remove("part")
+
+    assert len(assy.children) == 1
+    assert len(assy.objects) == 1