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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 post(self, *args):
 """ Start a new filewatcher at the specified path. """

        filepath = self.get_body_argument('filepath')
        if not self.fs.exists(filepath):
            raise tornado.web.HTTPError(404)

        Filewatcher.add_directory_to_watch(filepath)
        self.write({'msg':'Watcher added for {}'.format(filepath)})