Why another binding library?

The official Python bindings for openNURBS are provided by McNeel in the rhino3dm package, an open-source, large project which provides bindings for most, if not all, openNURBS classes. It also supports multiple programming languages. These capabilities come with a trade-off: increased complexity of both the source code and the accompanying documentation.

However, at the time of writing (November 2025), the documentation and type hints do not always accurately reflect the implementation, making the API difficult to discover and use effectively. While several improvements have been merged, significant gaps remain; as example refer to this forum thread.

A more fundamental limitation is that objects retrieved from or added to a model cannot be modified in place. Among many others, see discussions in #695 and in #649.

So what is different?

py3dm is a lightweight Python library that provides direct bindings to openNURBS classes. Its primary goal is to offer access to the core functionalities of openNURBS, without the additional abstraction layers present in rhino3dm. While py3dm does not aim for the same level of coverage or completeness as rhino3dm, it emphasizes transparency, minimal overhead, and direct interaction with the underlying C++ objects.

Where possible, direct bindings are exposed to Python, allowing users to manipulate openNURBS objects natively. To improve usability, a small number of helper classes (Tables) have been defined to facilitate common operations on 3dm models and their components, without obscuring the underlying API.

py3dm provides comprehensive type hints for all classes and methods, enabling better integration with IDEs and static type checkers like mypy or Pylance. In addition, test suites are included to ensure correctness and coverage of the bindings.

Very little of openNURBS is wrapped so far, but this library is being developed in a way that should make it as easy as possible to wrap more functionality as necessary. If you find that a function that you would like to use is not yet wrapped, please create a discussion or feel free to wrap it on your own and submit a pull request.