code: def proxy_headers(self, proxy):
          
          headers = {}
          username, password = get_auth_from_url(proxy)
  
          if username and password:
              headers['Proxy-Authorization'] = _basic_auth_str(username,
                                                               password)
  
          return headers
docs: 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.