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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_proxy(self, url):
 """ Get a proxy to use for a given URL, excluding any banned ones. :param str url: The URL for which to find an appropriate proxy. :return: A proxy to use for the URL, or the string 'DIRECT', which means a proxy is not to be used. Can be ``None``, which means to not attempt the request. :rtype: str|None """

        proxies = self.get_proxies(url)
        for proxy in proxies:
            if proxy == 'DIRECT' or proxy not in self._offline_proxies:
                return proxy