Replacing Boost.Python by Pybind11

[howetuft]

Replacing Boost.Python with Pybind11

Proposal Overview

This is a proposal to replace Boost.Python with Pybind11 for Python bindings in LuxCore.

Rationale

The rationale for this replacement is as follows:

• Dependency Management:

  • Boost.Python is a compiled dependency and is build-dependent on Python and Numpy. It must therefore be compiled for each Python Version (6), for each Platform (4), i.e. in 24 flavors. This eventually means 24 sets of dependencies to be provided for LuxCore build.
  • In contrast, Pybind11 is headers-only and does not depend on the Python version, reducing the dependency sets to just 4—one per platform.

• Compatibility Issues:

  • Currently, Boost.Python requires a patch to be compatible with Numpy 2. This patch is not available on ConanCenter and requires an in-house recipe, adding complexity and ongoing maintenance.
  • On the other hand, the standard version of Pybind11's Conan recipe is fully adequate and builds out-of-the-box.

• Performance and Ease of Use:

  • Pybind11 is generally lighter than Boost.Python in terms of both compilation time and final executable size. For more details, refer to the Pybind11 Benchmark.
  • Pybind11 does not require Numpy to be installed prior to the build process, as Numpy is not a build dependency for Pybind11, simplifying the setup.
  • Pybind11 supports STL containers out-of-the-box.

• Industry Adoption:

Pybind11 is widely used by many large projects that offer Python bindings, including Blender. It is becoming the standard tool for Python bindings in the C++ community.