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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 add_subroute(self, pattern: str) -> "URLDispatcher": """ create new URLDispatcher routed by pattern """

        return URLDispatcher(
            urlmapper=self.urlmapper,
            prefix=self.prefix + pattern,
            applications=self.applications,
            extra_environ=self.extra_environ)