build123d

0.10.0 verified Sat May 09 auth: no python

A Python CAD programming library for creating parametric 3D models using a scripting approach. Current version is 0.10.0, requiring Python >=3.10 and <3.14. It provides both algebra and builder modes for constructing solids, and is built on top of cadquery-ocp (OpenCascade Python bindings). Release cadence is irregular, with major versions around every few months.

pip install build123d

Common errors

error AttributeError: 'NoneType' object has no attribute 'location' ↓

cause The operation did not produce a shape (e.g., subtraction removed everything, or a cut was misaligned).

fix

Check your geometry operations – ensure the objects actually intersect or that you're not cutting the entire part away.

error ImportError: cannot import name 'show_object' from 'build123d' ↓

cause Older version of build123d or missing ocp_vscode for Jupyter viewing.

fix

Upgrade: pip install -U build123d; for viewing, install ocp_vscode: pip install ocp_vscode and use from build123d import show_object.

error OSError: [WinError 126] The specified module could not be found when importing build123d ↓

cause Missing C++ redistributables on Windows (OpenCascade DLLs not found).

fix

Install Microsoft Visual C++ Redistributable for Visual Studio 2015-2022 (x64).

error RuntimeError: Builder mode only allows one pending shape at a time ↓

cause Nested BuildPart or BuildSketch without proper context management.

fix

Ensure you're not nesting builder contexts incorrectly – use separate with blocks or close the inner context before starting another.

Warnings

breaking In v0.10.0, methods `is_null`, `is_valid`, `shape_type` were changed to properties – remove parentheses from calls like `shape.is_valid()` -> `shape.is_valid`. ↓

fix Change `shape.is_valid()` to `shape.is_valid`, `shape.is_null()` to `shape.is_null`, `shape.shape_type()` to `shape.shape_type`.

deprecated In v0.9.0, several previously deprecated items were removed, including old-style `S` prefix aliases (e.g., `Solid` instead of `S`). Check release notes for full list. ↓

fix Use current names: `Solid` instead of `S`, `Face` instead of `F`, etc.

gotcha VTK version conflict when upgrading from build123d <=0.8.0 to 0.9.0 or later – old VTK from cadquery-ocp can cause import errors. ↓

fix Either create a fresh virtual environment, or uninstall VTK and reinstall a compatible version: `pip uninstall vtk && pip install vtk==9.3.1`.

gotcha `show_object` only works with the ocp_vscode viewer; if not installed, you'll get an ImportError or runtime error. ↓

fix Install `pip install ocp_vscode` or use `export_stl`/`export_step` to save files.

Install

conda install -c conda-forge build123d

Imports

Box
```
from build123d import Box
```
Location
```
from build123d import Location
```
Cylinder
```
from build123d import Cylinder
```
Sphere
```
from build123d import Sphere
```
BuildPart
```
from build123d import BuildPart
```
export_stl
```
from build123d import export_stl
```
show_object
```
from build123d import show_object
```
In Jupyter/VSCode, you need the ocp_vscode extension to use show_object. Otherwise use export_stl.

Quickstart

Creates a 10x10x10 box and subtracts a cylinder from its top face. Then exports the result as STL.

from build123d import *

with BuildPart() as part:
    Box(10, 10, 10)
    with Locations((0, 0, 5)):
        Cylinder(radius=2, height=6, mode=Mode.SUBTRACT)

# Export to STL
export_stl(part.part, "example.stl")

# To view in Jupyter (requires ocp_vscode):
# show_object(part.part)