Imcompatibility with Python 3.12 #96

My programme with tkintertable worked fine with Python 3.79.
Now I changed to Python 3.12 and some extra console output and an error is produced.

The following code is (behalve print statements) silent in Python 3.79:

print("Start Test")
self.grid = MyTable(
    parent=self.gridFrame,
    data=None,
    rows=0,
    cols=6,
    height=70,
    showkeynamesinheader=True,
    selectedcolor="white",
    rowselectedcolor="white",
)

self.model = self.grid.model
print("End Test")

Console output (Python 3.79):

Start Test
End Test

in Python 3.12 the console output is:

Start Test
Did not find preferences!!!
could not save
could not save
End Test

Furtheron later on in the code there is an exception (only 3.12) that I couldn't track up to now:

Exception ignored in: <function Preferences.del at 0x0000020907271800>
Traceback (most recent call last):
File "C:\Python312\Lib\site-packages\tkintertable\Prefs.py", line 64, in del
self.save_prefs()
File "C:\Python312\Lib\site-packages\tkintertable\Prefs.py", line 136, in save_prefs
print ('could not save')
ValueError: I/O operation on closed file.

Unfortunately I have no clue when the error raises. I will debug a little more and try to narrow it down...
The dialog with the tkintertable is rebuild after the first run and then the error raises.