Bonsai error encountered?
│
├── Python ImportError / ModuleNotFoundError?
│   ├── "No module named 'blenderbim'" → §1.1 (rename migration)
│   ├── "No module named 'bpy'" → §1.2 (wrong Python environment)
│   └── "No module named 'bonsai'" → §1.3 (addon not installed)
│
├── AttributeError / RuntimeError on IFC operation?
│   ├── "NoneType has no attribute 'by_type'" → §2.1 (no IFC file loaded)
│   ├── "No entity with id X" → §2.2 (stale entity reference)
│   ├── "RuntimeError: No structural analysis view context" → §2.3 (missing context)
│   └── "'void' module" or "add_opening" → §2.4 (deprecated API)
│
├── IFC schema violation or validation failure?
│   ├── Missing IfcProject / IfcUnitAssignment → §3.1 (invalid project)
│   ├── Wrong spatial hierarchy (aggregate vs contain) → §3.2
│   ├── Missing representation context → §3.3
│   └── Singular vs list parameter error → §3.4 (v0.8+ API change)
│
├── Geometry / placement issue?
│   ├── Object moved but IFC placement unchanged → §4.1
│   ├── Geometry not visible after creation → §4.2
│   └── Geometry corruption after external edit → §4.3
│
├── Property set error?
│   ├── Properties not written to IFC → §5.1
│   ├── Pset values not appearing in UI → §5.2
│   └── Weight calculation returns None → §5.3
│
├── Operator poll failure (greyed out / RuntimeError)?
│   ├── No active IFC file → §6.1
│   ├── No active object / wrong selection → §6.2
│   ├── Wrong Blender mode (Edit vs Object) → §6.3
│   └── No active camera / drawing context → §6.4
│
├── Drawing generation error?
│   ├── Empty SVG output → §7.1
│   ├── Missing annotations → §7.2
│   ├── Sheet composition failure → §7.3
│   └── InkScape dependency error → §7.4
│
├── BCF workflow error?
│   ├── BcfStore initialization failure → §8.1
│   ├── Viewpoint coordinate mismatch → §8.2
│   └── Version conflict (v2 vs v3) → §8.3
│
└── Clash detection error?
    ├── Empty results on known conflicts → §9.1
    ├── Unsaved IFC file → §9.2
    └── Missing Group A/B definition → §9.3

1. Import and Environment Errors

§1.1 ModuleNotFoundError: blenderbim

Error: ModuleNotFoundError: No module named 'blenderbim'

Cause: Using pre-2024 import paths. Bonsai was renamed from BlenderBIM in v0.8.0 (September 2024).

Fix: Replace ALL blenderbim.* imports with bonsai.*:

Old (WRONG)	New (CORRECT)
`from blenderbim.bim.ifc import IfcStore`	`from bonsai.bim.ifc import IfcStore`
`import blenderbim.tool as tool`	`import bonsai.tool as tool`
`import blenderbim.core.spatial`	`import bonsai.core.spatial`

Rule: ALWAYS use bonsai.*. Operator bl_idname values (bim.*) did NOT change.

§1.2 ModuleNotFoundError: bpy

Error: ModuleNotFoundError: No module named 'bpy'

Cause: Running Bonsai scripts from system Python instead of Blender's bundled Python.

Fix: ALWAYS execute via Blender:

blender --background --python my_script.py

NEVER run python3 my_script.py for scripts importing bonsai.* or bpy.

§1.3 Bonsai Not Installed

Error: ModuleNotFoundError: No module named 'bonsai'

Diagnosis:

Verify Blender version is 4.2.0+ (Bonsai v0.8.x minimum)
Check addon is enabled: Edit > Preferences > Add-ons > search "Bonsai"
On Linux: verify GLIBC 2.34+ (ldd --version | head -1)

§1.4 Module Cache Corruption After Upgrade

Error: AttributeError or ImportError after upgrading Bonsai

Cause: Stale .pyc bytecode from previous version.

Fix:

find ~/.config/blender/4.2/scripts/addons/bonsai/ -name "__pycache__" -type d -exec rm -rf {} +

Then restart Blender completely.

2. IFC Runtime Errors

§2.1 NoneType Error on IFC Operations

Error: AttributeError: 'NoneType' object has no attribute 'by_type'

Cause: IfcStore.get_file() returns None — no IFC project is loaded.

Fix: ALWAYS guard IFC access:

model = IfcStore.get_file()
if model is None:
    raise RuntimeError("No IFC project loaded. Open an IFC file first.")

§2.2 Stale Entity Reference

Error: RuntimeError: No entity with id X or entity attributes return unexpected values.

Cause: Entity references become invalid after file reload, undo operations, or external file modification.

Fix: NEVER cache entity references across operations. ALWAYS re-query:

entity = model.by_id(step_id)  # Re-query each time

§2.3 Missing Representation Context

Error: RuntimeError: No structural analysis view context found or geometry creation fails silently.

Cause: Adding geometry or representations without required IfcGeometricRepresentationContext.

Fix: ALWAYS verify context exists before creating geometry:

import ifcopenshell.util.representation

body_context = ifcopenshell.util.representation.get_context(
    model, "Model", "Body", "MODEL_VIEW")
if not body_context:
    model_ctx = ifcopenshell.api.run("context.add_context", model,
        context_type="Model")
    body_context = ifcopenshell.api.run("context.add_context", model,
        context_type="Model", context_identifier="Body",
        target_view="MODEL_VIEW", parent=model_ctx)

§2.4 Deprecated void.add_opening

Error: Module void not found or add_opening does not exist.

Cause: void.add_opening() was replaced by feature.add_feature() in IfcOpenShell v0.8.0+.

Fix:

# WRONG
ifcopenshell.api.run("void.add_opening", model, opening=opening, element=wall)

# CORRECT
ifcopenshell.api.run("feature.add_feature", model, feature=opening, element=wall)

3. IFC Schema Violations

§3.1 Invalid Project Structure

Error: IFC validation failure — missing IfcProject or IfcUnitAssignment.

Cause: Creating IFC files with ifcopenshell.file() directly instead of the project API.

Fix: ALWAYS use the project creation API:

model = ifcopenshell.api.project.create_file(version="IFC4")
ifcopenshell.api.unit.assign_unit(model)

NEVER use ifcopenshell.file() directly — it skips IfcProject, unit assignment, and context creation.

§3.2 Wrong Spatial Relationship Type

Error: Elements appear in wrong hierarchy level or validation reports spatial errors.

Cause: Confusing IfcRelAggregates (spatial decomposition) with IfcRelContainedInSpatialStructure (element containment).

Decision tree:

Placing an element?
├── Physical element (wall, column, slab) into a storey?
│   └── spatial.assign_container (creates IfcRelContainedInSpatialStructure)
│
├── Spatial element (storey) into building?
│   └── aggregate.assign_object (creates IfcRelAggregates)
│
└── Building into site?
    └── aggregate.assign_object (creates IfcRelAggregates)

Rule: ALWAYS use spatial.assign_container for physical elements. ALWAYS use aggregate.assign_object for spatial hierarchy.

§3.3 Missing Representation Context

See §2.3. Every IFC project MUST have at least a Model/Body/MODEL_VIEW context before assigning geometry.

§3.4 Singular vs List Parameter (v0.8+ Breaking Change)

Error: KeyError or TypeError when calling relationship API functions.

Cause: IfcOpenShell v0.8+ changed singular parameters to lists.

Fix:

# WRONG (pre-v0.8 style)
ifcopenshell.api.run("spatial.assign_container", model,
    product=wall, relating_structure=storey)

# CORRECT (v0.8+ style)
ifcopenshell.api.run("spatial.assign_container", model,
    products=[wall], relating_structure=storey)

# WRONG
ifcopenshell.api.run("type.assign_type", model,
    related_object=wall, relating_type=wall_type)

# CORRECT
ifcopenshell.api.run("type.assign_type", model,
    related_objects=[wall], relating_type=wall_type)

Rule: ALWAYS pass lists to products, related_objects parameters, even for single entities.

4. Geometry and Placement Errors

§4.1 IFC Placement Not Synced After Move

Error: Object appears moved in Blender viewport but IFC IfcLocalPlacement retains old coordinates.

Cause: Blender transform operations (G key, obj.location = ...) do NOT auto-update IFC placement.

Fix: ALWAYS call after any transform change:

bpy.ops.bim.edit_object_placement()

§4.2 Geometry Not Visible After Creation

Diagnostic checklist:

Verify representation context exists (§2.3)
Verify geometry.assign_representation was called
Verify element is assigned to a spatial container
Verify Blender object was linked via tool.Ifc.link(entity, obj)

§4.3 Geometry Corruption From External Edit

Error: IFC data inconsistent with Blender viewport after editing .ifc file externally.

Cause: Editing the IFC file on disk while Blender has the project open.

Fix: NEVER edit .ifc files externally while Blender has them open. After external modification: File > Reload IFC Project.

5. Property Set Errors

§5.1 Properties Not Written to IFC

Error: Property values set in Blender UI or via obj.PsetProperties do not persist in IFC file.

Cause: Modifying Blender UI properties does NOT automatically write to IFC.

Fix: ALWAYS use ifcopenshell.api:

pset = ifcopenshell.api.run("pset.add_pset", model,
    product=wall, name="Pset_WallCommon")
ifcopenshell.api.run("pset.edit_pset", model,
    pset=pset, properties={"FireRating": "REI60"})

§5.2 Pset Values Not Appearing in UI

Cause: Bonsai data cache not refreshed after direct API modifications.

Fix: Purge the relevant data cache:

from bonsai.bim.module.pset.data import PsetData
PsetData.purge()

§5.3 Weight Calculation Returns None

Error: get_net_weight() or get_gross_weight() returns None or zero.

Cause: Pset_MaterialCommon.MassDensity not assigned to the element's material.

Fix: ALWAYS assign material density BEFORE running weight calculations.

6. Operator Poll Failures

Bonsai operators implement poll() classmethods that check prerequisites. When poll() returns False, operators are greyed out in UI and raise RuntimeError from Python.

§6.1 No Active IFC File

Symptom: Most bpy.ops.bim.* operators fail or are greyed out.

Fix: Load or create an IFC project first:

bpy.ops.bim.create_project(template="metric_m")
# OR
bpy.ops.bim.load_project(filepath="project.ifc")

§6.2 No Active Object or Wrong Selection

Symptom: Element-specific operators (edit placement, assign class) fail.

Fix: ALWAYS verify selection:

obj = bpy.context.active_object
if obj is None:
    raise RuntimeError("No active object selected")
if obj.BIMObjectProperties.ifc_definition_id == 0:
    raise RuntimeError("Active object has no IFC assignment")

§6.3 Wrong Blender Mode

Symptom: Operators that require Object mode fail in Edit mode (or vice versa).

Fix: Switch mode before calling:

if bpy.context.mode != 'OBJECT':
    bpy.ops.object.mode_set(mode='OBJECT')

§6.4 No Active Camera / Drawing Context

Symptom: Drawing operators (bim.create_drawing, bim.add_annotation) fail.

Fix: ALWAYS activate a drawing camera before calling drawing operators:

if bpy.context.scene.camera is None:
    raise RuntimeError("No active camera. Activate a drawing view first.")

7. Drawing Generation Errors

§7.1 Empty SVG Output

Diagnostic checklist:

Active camera MUST be orthographic (not perspective)
IFC data MUST be synced (sync=True in bim.create_drawing)
Drawing elements MUST be within camera frustum
has_linework and/or has_underlay MUST be enabled

§7.2 Missing Annotations

Cause: Annotations are ONLY generated for orthographic camera views.

Fix: NEVER use perspective cameras for annotated drawings. Verify camera type is ORTHO.

§7.3 Sheet Composition Failure

Cause: InkScape not installed or not on system PATH.

Fix: Install InkScape. Sheet composition and PDF/DXF export REQUIRE InkScape.

§7.4 Freestyle SVG Exporter Not Active

Error: FREESTYLE linework mode produces no output.

Fix: Enable the Freestyle SVG Exporter add-on in Blender preferences before using FREESTYLE mode.

8. BCF Workflow Errors

§8.1 BcfStore Initialization Failure

Cause: Accessing BcfStore.bcfxml directly instead of using the lazy initializer.

Fix: ALWAYS use BcfStore.get_bcfxml() for proper initialization and path resolution.

§8.2 Viewpoint Coordinate Mismatch

Cause: Viewpoint activation applies georeference offsets. Coordinate systems may differ between BCF source and loaded model.

Fix: Verify georeference settings match between the model that created the BCF and the model loading it.

§8.3 BCF Version Conflict

Error: Operations fail when mixing BCF v2.1 and v3.0 data.

Fix: NEVER mix BCF versions within a single file. The version is detected on load and MUST remain consistent.

Rule: ALWAYS configure BCFProperties.author before creating topics or comments. ALWAYS call bim.save_bcf_project to persist changes.

9. Clash Detection Errors

§9.1 Empty Results on Known Conflicts

Diagnostic checklist:

Verify IFC files are SAVED to disk (clash detection reads from disk, not memory)
Verify both Group A and Group B are defined with sources
Verify element filters are not excluding the conflicting elements
Verify clash_set.mode matches the conflict type (intersection vs clearance)

§9.2 Unsaved IFC File

Error: Clash detection runs but finds no clashes in recently modified geometry.

Cause: Clash detection operates on IFC files on disk, NOT the live Blender scene.

Fix: ALWAYS save the IFC file before running clash detection:

bpy.ops.bim.save_project()
bpy.ops.bim.execute_ifc_clash()

§9.3 Missing Group Definition

Error: Clash detection requires both Group A and Group B.

Fix: ALWAYS define both groups, even for intra-model clashes (e.g., structural vs MEP from the same file).

10. Data Synchronization Errors

§10.1 Viewport Not Updating After API Changes

Cause: Direct ifcopenshell.api calls do NOT trigger Blender viewport refresh.

Fix: After direct API modifications:

# For property changes: purge data cache
from bonsai.bim.module.pset.data import PsetData
PsetData.purge()

# For geometry changes: trigger representation update
bpy.ops.bim.update_representation(obj=obj.name)

§10.2 Threading Errors

Cause: IfcStore is NOT thread-safe. Bonsai operators require the main thread.

Fix: NEVER use threading with Bonsai operations. For deferred execution, use:

bpy.app.timers.register(my_deferred_function)

§10.3 Invalid References After Undo

Cause: Undo invalidates IfcStore.file and all cached entity references.

Fix: NEVER store entity references across undo operations. ALWAYS re-query after undo.

References

Related Skills

bonsai-core-architecture — Three-layer architecture, IfcStore, operator patterns
bonsai-syntax-elements — Element access patterns, entity-object mapping
bonsai-impl-project — Project creation, schema selection, units
bonsai-impl-modeling — Element creation pipeline, type system, materials
bonsai-impl-drawing — Drawing generation, annotations, sheets
bonsai-impl-qto — Quantity takeoff, calculator functions
bonsai-impl-bcf — BCF issue tracking workflows
bonsai-impl-clash — Clash detection workflows

Sources

Bonsai Docs, IfcOpenShell, OSArch, IfcOpenShell API

bonsai-errors-common

Bonsai Common Errors: Diagnostic & Recovery Guide

Quick Reference: Error Decision Tree