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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 _get_application(self, subdomain):
 """ Return a WSGI application for subdomain. The subdomain is passed to the create_application constructor as a keyword argument. :param subdomain: Subdomain to get or create an application with """

        with self.lock:
            app = self.instances.get(subdomain)
            if app is None:
                app = self.create_application(subdomain=subdomain)
                self.instances[subdomain] = app
            return app