* Errors like syntax and runtime errors in python are thrown as
exceptions. So for when we invoke onto the renderer thread to do some
work, we need to be able to catch those exceptions otherwise the whole
program dies. So over the execute, temporarily switch the thread into
a catching-exception mode, which then gets rethrown on the invoker's
thread.
* Note that BeginInvoke shouldn't be used by python since the callback
might happen after the execution has finished (there's no way to wait
at the moment).
* This means that e.g. decimal separator will always be . and similar
effects, which avoids the need to have culture specific formatting or
special-case handling around CSV export etc.
baldurk