A teacher I know wanted to give an exercise to the students that involves writing some code that uses a function to draw a tree. He was inspired by this other French teacher who uses Tkinter for his exercises.

His exercise was simple enough. Students have to make the computer draw a given tree. The solution is straightforward. Import an external Python file (that is given) which defines a function called dessine, write code to represent the given tree in Python, and then use the dessine function with that tree as an input. The function dessine then uses Tkinter to draw the tree.

My teacher friend wrote his answer to this exercise locally and the dessine function works perfectly. However, when he tried answering the exercise as a student would (i.e. using the French Education nationale servers), it wouldn’t work.

After some debugging, we found out that it was because Tkinter opens a new window from a different application in order to draw the tree. This is fine if you’re working locally but a security issue if you are using a browser-based app. Browser-based apps cannot (and should not be able to) open random applications in your file system.

After a quick search, we found that plotly seemed to be a good candidate. The advantage of plotly is that it was compatible of showing the drawings directly on Jupyter notebook. Unexpectedly, updating the dessine function from using Tkinter to plotly was easier than expected. The old dessine function uses some auxiliary functions to figure out the coordinates of the nodes and the line segments on the tree. Hence, it was only a matter of looking at the documenation of both libraries and translating them.

At the end of the day, everyone was happy. I learned about plotly and had a small little puzzle after dinner, my teacher friend was able to give the exercise, and I heard that there were audible “wows” in the classroom when the students saw the plotly graphs.

PS: Here are the codes: old tkinter version from French teacher, and my version.