Tkinter / Tcl callbacks, and return -code error

[Jeff Epler]

On Tue, Nov 05, 2002 at 08:29:47AM -0800, Steve Davis wrote:
> I am working with a package written in C and Tcl/Tk, with python
> bindings.  It allows me to set up some callback functions, which
> notify progress of long-running calculation, and can also cancel these
> calculations.  I have the callbacks calling python functions, (using
> Tkinter "register()" function), but I can't figure out how to cancel
> the calculations.
> 
> To cancel the calculations from Tcl, one is supposed to "return -code
> error".  Unfortunately, there doesn't seem to be a python mechanism to
> do this.  The closest I've come is by making a python object with no
> string representation, and returning that object.  This approach goes
> too far, though - I get:
> 
> Fatal Python error: PyThreadState_Get: no current thread
> Aborted
> 
> It doesn't seem like my approach should kill the python interpreter,
> but I may be misunderstanding something.
> 
> If it's relevant, I'm using the "snack" audio package
> (http://www.speech.kth.se/snack), and the "progress" callback
> functions available with various sound manipulations.
> 
> So, is there a way to do the equivalent of the Tcl "return -code
> error" from within python?  If not, is there some workaround?
> -- 
> http://mail.python.org/mailman/listinfo/python-list

It looks like raising an exception in a Python function called from TCL
should end up returning TCL_ERROR.  It appears that there's an
"adderrorinfo" method as well.

Jeff