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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _on_startup(self, *args):
 """ Called when the HTTP server start """

        yield from Controller.instance().start()
        # Because with a large image collection
        # without md5sum already computed we start the
        # computing with server start
        asyncio.async(Qemu.instance().list_images())