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In fact, I saw this problem when trying to delete the 
bindings made for a Canvas: I noticed that when refreshing 
several times a canvas by deleting, then recreating all 
the items (including the bindings), the occupied memory 
increased with no apparent reason. So I dived into 
Tkinter.py, and found out that Tcl commands were created 
for each binding, but were only deleted either when 
deleting the Canvas (which I couldn't do), or when calling 
the tag_unbind method with the tagOrId, the sequence *and* 
the Tcl command name. So I tried to get this command name 
by calling tag_bind, and saw that the result was not what 
I expected.
The solution to remember the result of the call to 
tag_bind creating the binding provides a solution to this 
problem. It may just be a bit strange to explicitely 
remember the bindings in the application, since Tk/Tkinter 
already remembers them. It may also seem strange to get 
via tag_bind something that is completely useless at the 
Python level...

Anyway, thanks a lot.