Working on the Arrow codebase 🧐#

Finding your way around Arrow#

The Apache Arrow repository includes implementations for most of the libraries for which Arrow is available.

Languages like GLib (c_glib/), C++ (cpp/), C# (csharp/), Go (go/), Java (java/), JavaScript (js/), MATLAB (matlab/), Python (python/), R (r/) and Ruby (ruby/) have their own subdirectories in the main folder as written here.

Rust has its own repository available here.

In the language-specific subdirectories you can find the code connected to that language. For example:

  • The python/ folder includes pyarrow/ folder which contains the code for the pyarrow package and requirements files that you need when building pyarrow.

    The pyarrow/ includes Python and Cython code.

    The pyarrow/ also includes test/ folder where all the tests for the pyarrow modules are located.

  • The r/ directory contains the R package.

Other subdirectories included in the arrow repository are:

  • ci/ contains scripts used by the various continuous integration (CI) jobs.

  • dev/ contains scripts useful to developers when packaging, testing, or committing to Arrow, as well as definitions for extended continuous integration (CI) tasks.

  • .github/ contains workflows run on GitHub continuous integration (CI), triggered by certain actions such as opening a PR.

  • docs/ contains most of the documentation. Read more on Helping with documentation.

  • format/ contains binary protocol definitions for the Arrow columnar format and other parts of the project, like the Flight RPC framework.

Bindings, features, fixes and tests#

You can read through this section to get some ideas on how to work around the library on the issue you have.

Depending on the problem you want to solve (adding a simple binding, adding a feature, writing a test, …) there are different ways to get the necessary information.

For all the cases you can help yourself with searching for functions via some kind of search tool. In our experience there are two good ways:

  1. Via GitHub Search in the Arrow repository (not a forked one) This way is great as GitHub lets you search for function definitions and references also.

  2. IDE of your choice.


The term “binding” is used to refer to a function in the C++ implementation which can be called from a function in another language. After a function is defined in C++ we must create the binding manually to use it in that implementation.


There is much you can learn by checking Pull Requests and unit tests for similar issues.

Adding a fix in Python

If you are updating an existing function, the easiest way is to run Python interactively or run Jupyter Notebook and research the issue until you understand what needs to be done.

After, you can search on GitHub for the function name, to see where the function is defined.

Also, if there are errors produced, the errors will most likely point you towards the file you need to take a look at.

Python - Cython - C++

It is quite likely that you will bump into Cython code when working on Python issues. It’s less likely is that the C++ code needs updating, though it can happen.

As mentioned before, the underlying code is written in C++. Python then connects to it via Cython. If you are not familiar with it you can ask for help and remember, look for similar Pull Requests and GitHub issues!

Adding tests

There are some issues where only tests are missing. Here you can search for similar functions and see how the unit tests for those functions are written and how they can apply in your case.

This also holds true for adding a test for the issue you have solved.

New feature

If you are adding a new future in Python you can look at the tutorial for ideas.

Philosophy behind R bindings

When writing bindings between C++ compute functions and R functions, the aim is to expose the C++ functionality via the same interface as existing R functions.

To read the full content on the topic of R bindings read through the Writing Bindings article.