Module Contents

class ifcopenshell.api.classification.add_reference.Usecase
add_from_library() ifcopenshell.entity_instance
get_existing_reference(identification: str | None = None) ifcopenshell.entity_instance | None
update_relationships(reference: ifcopenshell.entity_instance) None
ifcopenshell.api.classification.add_reference.add_reference(file: ifcopenshell.file, products: list[ifcopenshell.entity_instance], reference: ifcopenshell.entity_instance | None = None, identification: str | None = None, name: str | None = None, classification: ifcopenshell.entity_instance | None = None, is_lightweight=True) ifcopenshell.entity_instance | None

Adds a new classification reference and assigns it to the list of products

A classification reference is a single entry such as “Pr_12_23_34” that is part of an external classification system (such as Uniclass or Omniclass).

References can be added to almost any object in IFC, including physical objects, object types, properties, tasks, costs, resources, or even resources such as profiles, documents, libraries, and so on.

Classification references can be added in two ways. Option 1) specify a custom arbitrary reference, where you have to manually specify the identification (e.g. “Pr_12_23_45”) and name (e.g. “Door Products”). Option 2) add a reference from an IFC classification library. The latter is preferred if you are using a common classification system such as Uniclass, as the library will be prepopulated with all the valid classifications already.

Objects are allowed to have multiple classification references from multiple classification systems. This means that adding a new reference will not remove existing references.

References can be inherited from types. This means that if an IfcWallType has a classification reference of Pr_12_23_34, then all IfcWall occurrences of that type automatically get the same classification of Pr_12_23_34. This means that it is more efficient to assign to types where possible. If a classification reference is assigned to both the type and an occurrence, then the assignment at the occurrence will override the type classification.

  • product (list[ifcopenshell.entity_instance]) – The list of IFC objects, properties, or resources you want to associate the classification reference to.

  • reference (ifcopenshell.entity_instance, optional) – The classification reference entity taken from an IFC classification library. If you supply this parameter, you will use option 2.

  • identification (str, optional) – If you choose option 1 and do not specify a reference, you may manually specify an identification code. The code is typically a short identifier and may have punctuation to separate the levels of hierarchy in the classificaion (e.g. Pr_12_23_34).

  • name (str, optional) – If you choose option 1 and do not specify a reference, you may manually specify a name. The name is typically human readable.

  • classification (ifcopenshell.entity_instance) – The IfcClassification entity in your IFC model (not the library, if you are doing option 2) that the reference is part of.

  • is_lightweight (bool, optional) – If you are doing option 2, choose whether or not to only add that particular reference (lighweight) or also add all of its parent references in the classification hierarchy (not lighweight). For example, adding a lightweight reference to Pr_12_23_34 will only add Pr_12_23_34, but adding a heavy reference to Pr_12_23_34 will also add Pr_12_23 and Pr_12. These parent references merely help describe the “tree” of classifications, but is generally unnecessary. Using lightweight classifications are recommended and is the default.


TypeError – If file is IFC2X3 and products has non-IfcRoot elements.


The newly added IfcClassificationReference or None if products was empty list.

Return type:

Union[ifcopenshell.entity_instance, None]


# Option 1: adding and assigning a new reference from scratch
wall_type = model.by_type("IfcWallType")[0]
classification = ifcopenshell.api.run("classification.add_classification",
    model, classification="MyCustomClassification")
ifcopenshell.api.run("classification.add_reference", model,
    products=[wall_type], classification=classification,
    identification="W_01", name="Interior Walls")

# Option 2: adding a popular classification from a library
library = ifcopenshell.open("/path/to/Uniclass.ifc")
lib_classification = library.by_type("IfcClassification")[0]
classification = ifcopenshell.api.run("classification.add_classification",
    model, classification=lib_classification)
reference = [r for r in library.by_type("IfcClassificationReference")
    if r.Identification == "XYZ"][0]
ifcopenshell.api.run("classification.add_reference", model,
    products=[wall_type], classification=classification,