A null program - what is it doing?

[Gib Bogle]

No doubt a dumb question from a noob:

The following program (a cut down version of some test code) uses no CPU, and 
does not terminate:

import sys
from PyQt4.QtCore import *

if __name__=="__main__":
     app = QCoreApplication(sys.argv)
     sys.exit(app.exec_())

What is the program doing?  What is the correct way to terminate the execution?

Thanks in advance for educating me.