In principle one can use the reinitialize command (Run, Python Engine, 
Reinitialize) to interrupt the interpreter but this not only stops execution 
but resets the interpreter entirely. That means it forgets everything including 
the current directory, code loaded, variable asignments and so on.

For testing purposes it is useful to build up an environment in the 
interpreter and test individual functions. If for some reason the 
interpreter hangs (gets in an infinite loop, test data is too big to process 
and one gets bored waiting...) it is a nuisance to lose context when resetting 
the interpreter.