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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 proxy_headers(self, proxy):
 """Returns a dictionary of the headers to add to any request sent through a proxy. This works with urllib3 magic to ensure that they are correctly sent to the proxy, rather than in a tunnelled request if CONNECT is being used. This should not be called from user code, and is only exposed for use when subclassing the :class:`HTTPAdapter <requests.adapters.HTTPAdapter>`. :param proxies: The url of the proxy being used for this request. :param kwargs: Optional additional keyword arguments. """

        headers = {}
        username, password = get_auth_from_url(proxy)

        if username and password:
            headers['Proxy-Authorization'] = _basic_auth_str(username,
                                                             password)

        return headers