ifcos-errors-patterns

IfcOpenShell Error Patterns and Debugging

Quick Reference

Decision Tree: Diagnosing IfcOpenShell Errors

Error occurred?
├── RuntimeError
│   ├── "entity not found in schema" → Schema mismatch (§1)
│   ├── "Failed to process shape" → Geometry failure (§4)
│   ├── Entity reference invalid → Entity was removed (§5)
│   └── Invalid STEP data → File corruption (§7)
│
├── AttributeError
│   ├── "entity has no attribute 'X'" → Wrong attribute name / wrong entity type (§2)
│   ├── NoneType has no attribute → Null return not checked (§6)
│   └── 'parent' / 'children' → IFC uses relationships, not tree attributes (§3)
│
├── TypeError
│   ├── Wrong argument type to create_entity → Type mismatch in attributes (§8)
│   ├── Expected entity, got string → Entity reference required (§8)
│   └── Missing positional argument → settings missing for geom calls (§4)
│
├── ValueError
│   ├── GUID format wrong → Use ifcopenshell.guid.new() (§9)
│   └── Coordinate scale wrong → Unit conversion missing (§10)
│
└── Silent failures (no error but wrong output)
    ├── Orphaned entities → Missing relationship creation (§3)
    ├── Duplicate property sets → Not checking existing psets (§11)
    ├── Invalid file → Missing OwnerHistory in IFC2X3 (§12)
    └── Wrong spatial location → Missing spatial containment (§3)

Critical Warnings

• ALWAYS use ifcopenshell.api.run() for mutations. NEVER modify entity attributes directly for relationships, spatial containment, or property sets.
• ALWAYS check model.schema before using schema-specific entities. Entity names differ between IFC2X3, IFC4, and IFC4X3.
• ALWAYS check return values for None before accessing attributes. Functions like get_container(), get_type(), and create_shape() can return None.
• NEVER use model.remove() directly on products. Use ifcopenshell.api.run("root.remove_product", ...) to clean up relationships.
• NEVER cache entity references across file modifications. Entity wrappers become invalid after model.remove() or model.undo().
• NEVER assume coordinate units. ALWAYS call ifcopenshell.util.unit.calculate_unit_scale(model) and apply the scale factor.
• ALWAYS wrap geometry processing in try/except RuntimeError. Not all elements have processable geometry.

---

Error Category 1: Schema Mismatch Errors

IFC has three major schema versions with different entity names. Using an entity that does not exist in the file's schema raises RuntimeError.

# IfcOpenShell: schema-agnostic pattern
import ifcopenshell

model = ifcopenshell.open("model.ifc")
schema = model.schema  # "IFC2X3", "IFC4", or "IFC4X3"

# WRONG: IfcBuiltElement only exists in IFC4X3
element = model.create_entity("IfcBuiltElement", ...)
# RuntimeError: entity 'IfcBuiltElement' not found in schema 'IFC2X3'

# CORRECT: Check schema first
if schema == "IFC4X3":
    element = model.create_entity("IfcBuiltElement", ...)
else:
    element = model.create_entity("IfcBuildingElementProxy", ...)

Key entity differences by schema:

Entity/Concept	IFC2X3	IFC4	IFC4X3
Standard wall	IfcWallStandardCase	IfcWall	IfcWall
Building element base	IfcBuildingElement	IfcBuildingElement	IfcBuiltElement
OwnerHistory	REQUIRED	OPTIONAL	OPTIONAL
Door type	IfcDoorStyle	IfcDoorType	IfcDoorType
Window type	IfcWindowStyle	IfcWindowType	IfcWindowType
Infrastructure	Not available	Not available	IfcBridge, IfcRoad, IfcAlignment

---

Error Category 2: AttributeError on Entity Attributes

IFC entity attributes use PascalCase. Using wrong case or non-existent attribute names raises AttributeError.

# WRONG: snake_case or lowercase
wall.global_id       # AttributeError
wall.name            # AttributeError
wall.object_type     # AttributeError

# CORRECT: PascalCase as defined in IFC schema
wall.GlobalId        # "3Ks0WO3qP2xhJ0wBKg$u5H"
wall.Name            # "Wall 001"
wall.ObjectType      # "Standard Wall"

ALWAYS use element.get_info() to discover available attributes:

info = wall.get_info()
# Returns dict: {"id": 42, "type": "IfcWall", "GlobalId": "...", "Name": "...", ...}
print(list(info.keys()))  # See all attribute names

---

Error Category 3: Incorrect Relationship Handling

IFC uses objectified relationships (separate entities). There are NO parent/child attributes on elements.

# WRONG: IFC has no tree-style attributes
storey.parent = building        # AttributeError
wall.ContainedInStructure = storey  # Does NOT work as expected

# CORRECT: Use ifcopenshell.api for relationships
# Spatial hierarchy (aggregation): Project > Site > Building > Storey
ifcopenshell.api.run("aggregate.assign_object", model,
    products=[storey], relating_object=building)

# Elements in spatial container (containment)
ifcopenshell.api.run("spatial.assign_container", model,
    products=[wall], relating_structure=storey)

Relationship type reference:

Relationship	API Function	Purpose
IfcRelAggregates	aggregate.assign_object	Spatial hierarchy decomposition
IfcRelContainedInSpatialStructure	spatial.assign_container	Element in spatial container
IfcRelDefinesByType	type.assign_type	Element to Type assignment
IfcRelDefinesByProperties	pset.add_pset	Property set to element
IfcRelAssociatesMaterial	material.assign_material	Material to element
IfcRelVoidsElement	void.add_opening	Opening in element

---

Error Category 4: Geometry Processing Failures

ifcopenshell.geom.create_shape() invokes OpenCASCADE and can fail for multiple reasons.

import ifcopenshell.geom

settings = ifcopenshell.geom.settings()
settings.set(settings.USE_WORLD_COORDS, True)

# ALWAYS wrap in try/except
try:
    shape = ifcopenshell.geom.create_shape(settings, element)
except RuntimeError as e:
    print(f"Geometry failed for {element.is_a()} #{element.id()}: {e}")
    shape = None

# ALWAYS check result before accessing geometry data
if shape is not None:
    verts = shape.geometry.verts
    faces = shape.geometry.faces

Common geometry failure causes:

Cause	Symptom	Fix
No Representation	RuntimeError	Check element.Representation is not None
Missing settings argument	TypeError	Pass settings as first argument
Spatial element (IfcSite)	RuntimeError	Filter by elements with Body representation
Complex boolean operations	RuntimeError	Set DISABLE_OPENING_SUBTRACTIONS=True
Corrupt geometry definition	RuntimeError	Skip element, log warning

Check for geometry before processing:

def has_geometry(element):
    """Check if an IFC element has processable 3D geometry."""
    if not hasattr(element, "Representation") or element.Representation is None:
        return False
    for rep in element.Representation.Representations:
        if rep.RepresentationIdentifier in ("Body", "Facetation", "Tessellation"):
            return True
    return False

---

Error Category 5: Entity Invalidation After Removal

Entity wrappers are C++ pointers. After model.remove(), references become invalid.

wall = model.by_type("IfcWall")[0]
wall_id = wall.id()
wall_name = wall.Name  # Works fine

model.remove(wall)
# wall is NOW INVALID: the C++ object is destroyed

# WRONG: Using invalidated reference
print(wall.Name)   # RuntimeError or undefined behavior
print(wall.id())   # RuntimeError or undefined behavior

# CORRECT: Extract needed data BEFORE removal
wall_data = {"id": wall.id(), "name": wall.Name, "guid": wall.GlobalId}
ifcopenshell.api.run("root.remove_product", model, product=wall)
# Use wall_data (plain dict) from here

NEVER iterate and remove simultaneously:

# WRONG: Modifying collection while iterating
for wall in model.by_type("IfcWall"):
    model.remove(wall)  # Invalidates the iteration!

# CORRECT: Collect first, then remove
walls_to_remove = list(model.by_type("IfcWall"))
for wall in walls_to_remove:
    ifcopenshell.api.run("root.remove_product", model, product=wall)

---

Error Category 6: None Return Values Not Checked

Many IfcOpenShell utility functions return None when data is not found.

import ifcopenshell.util.element

# WRONG: Assuming result is always valid
container = ifcopenshell.util.element.get_container(wall)
print(container.Name)  # AttributeError if container is None!

element_type = ifcopenshell.util.element.get_type(wall)
print(element_type.Name)  # AttributeError if no type assigned!

# CORRECT: ALWAYS check for None
container = ifcopenshell.util.element.get_container(wall)
if container is not None:
    print(container.Name)

element_type = ifcopenshell.util.element.get_type(wall)
if element_type is not None:
    print(element_type.Name)

Functions that commonly return None:

Function	Returns None When
get_container(element)	Element has no spatial containment
get_type(element)	No type assigned
get_material(element)	No material assigned
get_psets(element).get("X")	Property set does not exist
geom.create_shape(settings, element)	Geometry processing fails
model.by_guid("...")	GUID not found in file

---

Error Category 7: File Corruption from Direct Removal

Using model.remove() directly leaves dangling references in relationship entities.

# WRONG: Direct removal corrupts relationships
model.remove(wall)
# IfcRelContainedInSpatialStructure still references the removed wall
# IfcRelDefinesByProperties still references the removed wall
# File is NOW CORRUPTED

# CORRECT: API handles all relationship cleanup
ifcopenshell.api.run("root.remove_product", model, product=wall)
# Removes wall + cleans up:
# - Spatial containment relationships
# - Property set relationships
# - Material associations
# - Opening relationships
# - Type assignments
# - Placement (if not shared)
# - Representation (if not shared)

---

Error Category 8: TypeError from Wrong Attribute Types

IFC attributes have strict types. Passing wrong types raises TypeError or RuntimeError.

# WRONG: String where entity is expected
wall.ObjectPlacement = "at origin"
# RuntimeError: Expected IfcObjectPlacement, got str

# WRONG: Single entity where tuple is expected
rel.RelatedElements = wall  # Expects tuple, not single entity

# CORRECT: Use proper entity references
placement = model.create_entity("IfcLocalPlacement", ...)
wall.ObjectPlacement = placement

# CORRECT: Use tuple for aggregate attributes
rel.RelatedElements = (wall1, wall2)

---

Error Category 9: GUID Format Errors

IFC uses 22-character base64 GUIDs, NOT standard 36-character UUIDs.

import uuid

# WRONG: Standard UUID format
wall = model.create_entity("IfcWall",
    GlobalId=str(uuid.uuid4()),  # 36 chars — WRONG format
    Name="Wall")

# CORRECT: Use ifcopenshell.guid
wall = model.create_entity("IfcWall",
    GlobalId=ifcopenshell.guid.new(),  # 22 chars — correct
    Name="Wall")

# BEST: Use ifcopenshell.api (auto-generates GUID)
wall = ifcopenshell.api.run("root.create_entity", model,
    ifc_class="IfcWall", name="Wall")

---

Error Category 10: Unit Conversion Errors

IFC files can use meters, millimeters, feet, or other units. NEVER assume meters.

import ifcopenshell.util.unit

# ALWAYS get the unit scale factor
unit_scale = ifcopenshell.util.unit.calculate_unit_scale(model)
# mm file → 0.001, m file → 1.0, ft file → 0.3048

# Apply to ALL coordinates extracted from the model
raw_coords = [3500.0, 2800.0, 0.0]  # From IFC file
coords_meters = [c * unit_scale for c in raw_coords]

---

Error Category 11: Duplicate Property Sets

Creating a property set without checking for existing ones produces duplicates.

from ifcopenshell.util.element import get_psets

# WRONG: Creates duplicate if Pset_WallCommon already exists
pset = ifcopenshell.api.run("pset.add_pset", model,
    product=wall, name="Pset_WallCommon")

# CORRECT: Check first, then create or update
existing = get_psets(wall)
if "Pset_WallCommon" in existing:
    pset = model.by_id(existing["Pset_WallCommon"]["id"])
else:
    pset = ifcopenshell.api.run("pset.add_pset", model,
        product=wall, name="Pset_WallCommon")

ifcopenshell.api.run("pset.edit_pset", model,
    pset=pset, properties={"IsExternal": True})

---

Error Category 12: Missing OwnerHistory in IFC2X3

OwnerHistory is REQUIRED on most entities in IFC2X3 but OPTIONAL in IFC4/IFC4X3.

# WRONG: No OwnerHistory in IFC2X3
model = ifcopenshell.file(schema="IFC2X3")
wall = model.create_entity("IfcWallStandardCase",
    GlobalId=ifcopenshell.guid.new(), Name="Wall")
# File is INVALID: validators will reject it

# CORRECT: Use ifcopenshell.api (handles OwnerHistory automatically)
model = ifcopenshell.file(schema="IFC2X3")
wall = ifcopenshell.api.run("root.create_entity", model,
    ifc_class="IfcWallStandardCase", name="Wall")
# API creates OwnerHistory and assigns it automatically

---

Debugging Strategy

Step-by-step Debugging Protocol

import ifcopenshell

def debug_ifc_element(model, element):
    """Comprehensive debug output for an IFC element."""
    print(f"=== Debug: {element.is_a()} #{element.id()} ===")
    print(f"Schema: {model.schema}")
    print(f"GlobalId: {element.GlobalId}")
    print(f"Name: {element.Name}")

    # 1. Check all attributes
    info = element.get_info()
    for key, value in info.items():
        print(f"  {key}: {value}")

    # 2. Check spatial containment
    container = ifcopenshell.util.element.get_container(element)
    print(f"Container: {container.Name if container else 'NONE (PROBLEM!)'}")

    # 3. Check type assignment
    elem_type = ifcopenshell.util.element.get_type(element)
    print(f"Type: {elem_type.Name if elem_type else 'None'}")

    # 4. Check property sets
    psets = ifcopenshell.util.element.get_psets(element)
    print(f"Property sets: {list(psets.keys())}")

    # 5. Check geometry
    if hasattr(element, "Representation") and element.Representation:
        reps = [r.RepresentationIdentifier
                for r in element.Representation.Representations]
        print(f"Representations: {reps}")
    else:
        print("Representations: NONE")

Common Debug Techniques

# Inspect entity type hierarchy
print(element.is_a())           # "IfcWall"
print(element.is_a("IfcRoot"))  # True (checks inheritance)

# List all entities of a type
walls = model.by_type("IfcWall")
print(f"Total walls: {len(walls)}")

# Find entity by GlobalId
entity = model.by_guid("3Ks0WO3qP2xhJ0wBKg$u5H")

# Find entity by step ID
entity = model.by_id(42)

# Get inverse relationships (who references this entity?)
refs = model.get_inverse(wall)
for ref in refs:
    print(f"Referenced by: {ref.is_a()} #{ref.id()}")

# Validate file units
unit_scale = ifcopenshell.util.unit.calculate_unit_scale(model)
print(f"Unit scale to meters: {unit_scale}")

# Check file statistics
print(f"Total entities: {len(model)}")
for entity_type in ["IfcWall", "IfcSlab", "IfcColumn", "IfcBeam"]:
    count = len(model.by_type(entity_type))
    if count > 0:
        print(f"  {entity_type}: {count}")

---

Reference Links

• Error Handling Methods — Exception types, validation functions, diagnostic utilities
• Working Debug Examples — End-to-end error handling and debugging code
• Anti-Patterns — Common IfcOpenShell mistakes with corrections