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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):
 """Start server if not previously started."""

        msg = ''
        if not self.running():
            if self._port == 0:
                self._port = _port_not_in_use()
            self._process = start_server_background(self._port)
        else:
            msg = 'Server already started\n'
        msg += 'Server running at {}'.format(self.url())
        print(msg)