Éric, I think your suggestions are all good ones, and I have incorporated them into the file. (But do note that the departures we are now making from Ned's own copy of the tracer code ­— removing the commented-out debugging statement, and the long comment, and the inheritance from object — might make it harder to bring in changes from his own copy if he should ever further improve it.) I have tried to write the comments to be more informative, while also addressing your own ideas; let me know if you like the result!

Oh: and, I am continuing to use this new file in my own work on the Python core, and it has been working fine — so no problems with the actual code have developed over these first 3+ months of use.