Support for the Jupyter Debugger Protocol just landed in ipykernel

JupyterLab 3.0 includes a visual debugger that allows to interactively set breakpoints, step into functions, and inspect variables with any Jupyter kernel that implements the Jupyter debugger protocol.

The first two language kernels to implement the new protocol were xeus-python (a Python kernel) and xeus-robot (a kernel for Robot Framework). Unfortunately, the reference Python kernel, ipykernel, did not support debugging yet, until now!

Today, we are pleased to announce that debugging support landed in ipykernel, and will be available in the next major release, ipykernel 6.0. Pre-releases including the ipykernel debugger are available.

What will change with ipykernel 6.0?

Enabling support for debugging in ipykernel required important changes in the code base regarding the concurrency model of the kernel. The main change is that the processing of messages on the "control channel" now happens in a different thread, allowing for the processing to happen while user code is running.

Ipykernel 6.0 includes several other updates. Tornado coroutines were dropped in favor of native coroutines. The Matplotlib inline backend was split into a separate package, and ipykernel depends on debugpy, an implementation of the Debug Adapter Protocol for Python.

If you are interested in testing out the new features, check out the beta release!

pip install ipykernel --pre

Try it now!

Thanks to MyBinder, you can also try it out without the need of installing anything on your computer. Just follow this link:

What about the future?

A lot of new features are in the works with the JupyterLab debugger.

• JupyterLab 3.1 will include several usability improvements to the debugger.
• It will also add the ability to submit code for execution when stopped at a breakpoint.
• We are working on a richer variable explorer, using Jupyter's rich display system to enable the rich-rendering of variables in the explorer, to e.g. render dataframes as tables.

Finally, we also plan on adding debugging support to other language kernels.

Acknowledgements

The work of Johan and Sylvain at QuantStack on the debugger support in ipykernel was funded by Two Sigma. We are greateful to Min Ragan Kelley and Matthias Bussonnier, who reviewed the pull requests on debugger support.

About the authors

Johan Mabille is a scientific software developer at QuantStack.

Johan is very active in the Jupyter ecosystem, as the creator of xeus, a C++ implementation of the Jupyter protocol, and several language kernels, such as xeus-python, xeus-cling, and xeus-robot. Johan also made contributions to the Jupyter widgets ecosystem and to JupyterLab.

Sylvain Corlay is the founder and CEO of QuantStack.

As an open-source developer, Sylvain is very active in the Jupyter project with contributions in several components of the stack, including widgets, kernels, nbconvert, and others. He is also a steering committee member of the project.

Sylvain also does volunteer work for the community, as member of board of directors of NumFOCUS, co-organizer of the PyData Paris Meetup, and vice-chair of JupyterCon 2020.