PY-CLAS0009 · duplicate_component_attribute_alias_count

Keep retained components as the single source of truth for their attributes.

This is a deterministic rule for python. Read its implementation.

Definition

Inspect class constructors and Pydantic model_post_init methods. When an owner retains a parameter as one field, report other fields assigned directly from attributes of that same parameter. self.document = document followed by self.path = document.path creates two access paths for one fact and lets later changes drift. Keep self.document and read self.document.path where needed.

Evidence

Each finding identifies the retained component, copied attribute, alias field, class, and exact assignment range. The result is the number of direct forwarded aliases. The value is the number of fields assigned directly from an attribute of a retained component.

Exceptions

Derived values such as self.name = normalize(document.path.name) are not direct aliases. Extracting a field is accepted when the owner does not retain the source component. Dynamic assignments, properties, descriptors, and nested helper scopes are not guessed.

Examples

Bad

`self.document = document` followed by `self.path = document.path` duplicates composition
state.

Good

Store only self.document = document and use self.document.path. If only the path is needed, store self.path = document.path without retaining the whole document.

References

• Adapts Pylint R0902 too-many-instance-attributes
• Cites “A Philosophy of Software Design”, chapter 5, information hiding
• Cites “Pydantic documentation”, faux immutability. Open reference