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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 start(self):
        ''' Install the Bokeh Server and its background tasks on a Tornado
        ``IOLoop``.

        This method does *not* block and does *not* affect the state of the
        Tornado ``IOLoop``  You must start and stop the loop yourself, i.e.
        this method is typically useful when you are already explicitly
        managing an ``IOLoop`` yourself.

        To start a Bokeh server and immediately "run forever" in a blocking
        manner, see :func:`~bokeh.server.server.BaseServer.run_until_shutdown`.

        '''
        assert not self._started, "Already started"
        self._started = True
        self._tornado.start()