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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 find_existing(self):
 """ Searches for existing server instances with matching tags. To match, the existing instances must also be "running". """

        instances = self.consul.find_servers(self.tags)
        maxnames = len(instances)
        while instances:
            i = instances.pop(0)
            server_id = i[A.server.ID]
            if self.namespace.add_if_unique(server_id):
                log.info('Found existing server, %s' % server_id)
                self.server_attrs = i
                break
            if len(self.namespace.names) >= maxnames:
                break
            instances.append(i)