Does anyone know if PyThreadState_SetAsyncExc stops a thread while its inside a native extension ? I'm trying to stop a testing script that boils down to this: while True: print "aaa" native_extension_call() print "bbb" Using PyThreadState_SetAsyncExc the module doesn't stop but if I add more print statements to increase the chance that PyThreadState_SetAsyncExc is called when the module is executing Python code, the module stops.