Cascade Step File Demo

[Brock Birdsong]

I'm trying to run the Cascade demo to import a STEP file and I received the following error message:

(chrono_test) PS C:\Users\birds\.conda\pkgs\pychrono-9.0.1-py312h84d2775_0\Lib\site-packages\pychrono\demos\cascade> python .\demo_CAS_stepfile.py
Traceback (most recent call last):
  File "C:\Users\birds\.conda\pkgs\pychrono-9.0.1-py312h84d2775_0\Lib\site-packages\pychrono\demos\cascade\demo_CAS_stepfile.py", line 16, in <module>
    from OCC.Core  import TopoDS
ModuleNotFoundError: No module named 'OCC'

I followed the 16 Nov 2025 directions posted by Uebian.

Suggestions?

[dr.ratz...@gmail.com]

Seems, you don't have the python-occ module. It is needed to use OpenCascade functions in Python.

[Bocheng Zou]

Hi Brock,

Unfortunately, we decided not to include the cascade support for the upcoming Chrono 10 conda package. It's because there's an incompatibility between the SWIG version we used and the SWIG version that the upstream pythonocc-core on conda-forge uses. Specifically, we are using SWIG 4.3 (SWIG_RUNTIME_VERSION=4), while pythonocc-core is using SWIG 4.4 (SWIG_RUNTIME_VERSION=5). 

However, you can still use the cascade module in PyChrono by compiling both Project Chrono and pythonocc-core( https://github.com/tpaviot/pythonocc-core ) from source.

Best,

Bocheng Zou

On 3/14/26 04:53, Brock Birdsong wrote:

Thanks for the quick response! I can wait for the update in a few days. 

Brock

On Fri, Mar 13, 2026 at 23:52 Bocheng Zou <bzo...@wisc.edu> wrote:

Hi Brock,

Thank you for reaching out! I was recently aware of that there are issues related with the OCCT in our released conda packages, and I'm working on a fix. A new conda package with that fix is expected to be released in 3 days. 

If you urgently need to use the cascade module with PyChrono, it's recommended to compile both project chrono and pythonocc-core ( https://github.com/tpaviot/pythonocc-core ) from scratch instead of using the conda package. 

Best,

Bocheng Zou

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