# Custom build steps: PyVista on ARM64 example

**URL:** <https://si-tesseract.discourse.group/t/custom-build-steps-pyvista-on-arm64-example/54>\
**Category:** Showcase\
**Created:** [February 27, 2025, 9:31am UTC](https://si-tesseract.discourse.group/t/custom-build-steps-pyvista-on-arm64-example/54 "2025-02-27T09:31:09Z")\
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**Author:** ![Alessandro](https://yyz1.discourse-cdn.com/flex009/user_avatar/si-tesseract.discourse.group/alessandro/32/37_2.png) [@Alessandro](https://si-tesseract.discourse.group/u/Alessandro)\
**Post date:** [February 27, 2025, 9:31am UTC](https://si-tesseract.discourse.group/t/custom-build-steps-pyvista-on-arm64-example/54/1 "2025-02-27T09:31:09Z")

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# Custom build steps: PyVista on ARM64 example

## Context

Tesseracts use by default an official Python docker image as the base image. Although this covers many useful cases, some system dependencies sometimes require a custom image and extra build steps.

## Example yaml

Via `tesseract_config.yaml`, it is possible to somewhat flexibly alter the build process to accomodate different needs. As a concrete example, here’s what we had to do internally in order to to build an arm64 Tesseract with PyVista installed as a dependency:

```auto
build_config:
  base_image: "debian:trixie"

  target_platform: "linux/arm64"

  extra_packages:
   - python3-vtk9
   - python3-venv

  custom_build_steps:
    - |
      USER root
      # Symlink the VTK Python bindings into the Python site-packages directory
      RUN python_site=$(python -c "import site; print(site.getsitepackages()[0])") && \
          ln -s /usr/lib/python3/dist-packages/vtk* $python_site && \
          ls -l $python_site/vtk* && \
          python -c "import vtk"
      # Must install pyvista with --no-deps to avoid installing vtk (which we copied from the system)
      RUN pip install matplotlib numpy pillow pooch scooby && pip install --no-deps pyvista==0.44.1
      USER tesseractor

```

Here is what the various configurations set above do to the build process:

- We started from a base image that had VTK 9.2 installed (`debian:trixie`), which was specified via `base_image`.
- The `target_platform` is set to `linux/arm64`, which will build the resulting image for an ARM64 architecture.
- We installed python3-vtk9 and python3-venv to get the VTK Python bindings and `venv` by specifying them in `extra_packages`. You can think of `extra_packages` as a list of packages which are `apt-get install`ed right on the base image just immediately after some other dependencies (like `git`, `ssh`, and `build-essential`) are installed.
- We can then run arbitrary commands on the image which is being built via `custom_build_steps`. This list of commands need to be specified as if they were in a Dockerfile. In particular, we start here by temporarily setting the user to `root`, as the default user in the Tesseract build process is `tesseractor` – which does not have root privileges – and then switch back to the `tesseractor` user at the very end. We then run commands directly on the shell via `RUN` commands. All these steps specified in `custom_build_steps` are executed at the very end of the build process, followed only by a last execution of `tesseract-runtime check` that checks that the runtime can be launched and the user-defined `tesseract_api` module can be imported.