[Tkinter-discuss] Moving object on page leaves afterimage on Python 3 but not on 2

[Reinis Danne]

Hi!

I'm porting a chemistry drawing program BKChem [1] to Python 3
using the shared codebase between versions 2 and 3. It is working
fine on Python 2, but if I run it with Python 3 I have an issue
with redrawing the page.

The issue is that if I move an object by mouse then it leaves an
image of the object in the old place while moving the object to
the new place (Python 3). There is no such afterimage with Python
2. Similar effect can be achieved if object is deleted or its
creation is undoed - object is removed, but lines remain. It
seems that text is updated correctly, only bonds (lines) have the
issue.

Any ideas where the bug might be and how to debug it? As far as I
understand the moving of the object and updating the drawing is
up to tkinter or the underlying tk. It could be an issue with the
app losing track of the object, but in that case it wouldn't
create new lines (if I drag and drop an object several times,
several afterimages remain, but not 100% of the time; usually the
very first move works, but later ones produce the afterimages).
So I think it is a lower level issue.

To test:
$ git clone https://gitlab.com/bkchem/bkchem.git
$ cd bkchem
$ git submodule init
$ git submodule update
$ python3 bkchem/bkchem.py


Regards,
Reinis

[1] https://gitlab.com/bkchem/bkchem