Use CPython scripting when you want fast automation, data extraction, computational geometry, reporting, debugger support, or package-heavy workflows inside the host.

This page covers the modern CPython path: PythonNet in-process with CAD/BIM hosts. For IronPython, C#/F# scripts, and assemblies, see Execution Overview.

Claimed hosts for CPython today: Revit and the AutoCAD-family (AutoCAD, Civil 3D, Architecture, MEP, Electrical, Mechanical, Map 3D, Plant 3D).

In the current product lineup, only Plant 3D ships an embedded CPython runtime. All other claimed hosts use a Pixi-owned interpreter.

In-process CPython from Pixi. pixi.toml pins python = "3.14.*". Environment: %APPDATA%\RevitDevTool\pixi-env. PEP 723 packages install through Pixi (conda-forge + PyPI). If Pixi cannot run, pip / pyRevit cengines is the fallback.

Plant 3D is an AutoCAD-family vertical — the only one that embeds CPython before the add-in loads. RevitDevTool attaches pythonnet to the host python3xx.dll and never starts a second in-process interpreter (a Pixi 3.14 DLL would crash). PEP 723 packages install into a uv sidecar at %APPDATA%\RevitDevTool\uv-env\{major.minor} (often 3.13), then site.addsitedir overlays that prefix. Pixi is not used on this path. If uv cannot run, pip matching the host minor via pyRevit cengines is the fallback.

See the Plant 3D example for the Plant-specific workflow.

CPython script folders are discovered through files ending with:

*script.py

Example (repo path):

samples/PythonDemo/commands/data_analysis_script.py

Browse samples on GitHub: PythonDemo/commands

Dependencies are declared with PEP 723 metadata in the script file:

# /// script
# dependencies = ["polars", "numpy"]
# ///

The runtime parses metadata before execution and prepares the environment with Pixi on every claimed host except Plant 3D, which uses the uv sidecar.

Scripts receive __revit__ (UIApplication) and a shared state namespace on sys.__devtool__ for scope-local RevitDevTool state.

There is no __revit__. Use the host Application API instead. See AutoCAD Features for the AutoCAD host context pattern.

For modeless UI or background work in any host, route host API calls through the supported host execution path.

Python debugging uses debugpy and the debugger bridge. Configure VSCode attach, start the debugger, then run the script from RevitDevTool.

For the full workflow, port settings, .NET attach for scripts/assemblies, and troubleshooting, see Attach Debugger.

These suffixes serve different purposes — do not mix them:

*_ipy_script.py is for commands you run from RevitDevTool. test_*_ipy.py is how the pytest plugin routes IronPython unittest files to the host — it is not an execution entry name.

Current Python samples live under:

samples/PythonDemo/commands/

Notable examples:

• data_analysis_script.py
• dashboard_script.py
• debugpy_script.py
• selectionfilter_script.py
• visualization_curve_script.py
• visualization_solid_script.py
• visualization_xyz_script.py
• logging_format_script.py
• modeless_script.py

• Package installation can be blocked by local policy, a missing pixi executable (or uv on Plant 3D), or network access.
• On Plant 3D, host-owned attach cannot load conda Library\bin activation or a second in-process Python layout — prefer PyPI wheels with private native deps.
• Host API calls still require valid host context.
• PythonNet behavior differs from IronPython, especially around .NET interop.

• Attach Debugger
• Execution Overview
• Python Ecosystems
• IronPython — pyRevit Folder Compatibility