Fix invalid UniqueConstraint error message when loading a TypedTree

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## 0.6.1 (unreleased)
 - Add optional `tree.print(..., file=IO)` argument.
+- Fix invalid UniqueConstraint error message when loading a TypedTree.
 
 ## 0.6.0 (2023-11-01)
 

docs/sphinx/user_guide.rst

@@ -58,7 +58,7 @@ node_id (int, readonly):
   It cannot be changed later.
 
 kind (str, readonly):
-  Used by :class:`~nutree.typed_tree.TypedNode` (see `Typed child nodes <ug_graphs.html>`_).
+  Used by :class:`~nutree.typed_tree.TypedNode` (see :ref:`Typed child nodes <typed-tree>`).
 
 .. General API
 .. -----------

nutree/typed_tree.py

@@ -271,7 +271,7 @@ def add_child(
                 raise ValueError("Cannot set ID for deep copies.")
             source_node = child
             if source_node._tree is self._tree:
-                if source_node._parent is self._parent:
+                if source_node._parent is self:
                     raise UniqueConstraintError(
                         f"Same parent not allowed: {source_node}"
                     )
@@ -665,12 +665,16 @@ def iter_by_type(self, kind: Union[str, ANY_KIND]) -> Iterator[TypedNode]:
     @classmethod
     def _from_list(cls, obj: List[Dict], *, mapper=None) -> TypedTree:
         tree = cls()
+
+        # System root has index #0:
         node_idx_map = {0: tree._root}
+
+        # Start reading data lines starting at index #1:
         for idx, (parent_idx, data) in enumerate(obj, 1):
             parent = node_idx_map[parent_idx]
             # print(idx, parent_idx, data, parent)
             if type(data) is str:
-                # this can only happen if the source was generate by a plain Tree
+                # This can only happen if the source was generated by a plain Tree
                 n = parent.add(data, kind=DEFAULT_CHILD_TYPE)
             elif type(data) is int:
                 first_clone = node_idx_map[data]
@@ -683,7 +687,7 @@ def _from_list(cls, obj: List[Dict], *, mapper=None) -> TypedTree:
                 data_obj = call_mapper(mapper, parent, data)
                 n = parent.add(data_obj, kind=kind, data_id=data_id)
             elif isinstance(data, dict) and "str" in data:
-                # this can happen if the source was generate by without a
+                # This can happen if the source was generated without a
                 # serialization mapper, for a TypedTree that has str nodes
                 n = parent.add(data["str"], kind=data.get("kind"))
             else: