How can you assign weights to arrows in tkinter like in a FSM?

Question

I am fairly new to Python and especially Tkinter. I have set a goal for myself to make a GUI similar to

http://madebyevan.com/fsm/

I feel like this is an interesting machine that will give me some good insight into how to use tkinter. I have spent most of the day recreating certain aspects of this machine but have gotten stuck on an important feature.

I need to be able to add weights to my lines. I have no clue how to add a weight to the line the user can change. I have found that just using text, I can assign a number upon creation of the line but no clue how to have the user interact with this value.

Any key terms to search, packages to use, or even potentially some code would be greatly appreciated!