code: def _prepare_proxy(self, conn):
          
          # Python 2.7+
          try:
              set_tunnel = conn.set_tunnel
          except AttributeError:  # Platform-specific: Python 2.6
              set_tunnel = conn._set_tunnel
  
          if sys.version_info <= (2, 6, 4) and not self.proxy_headers:  # Python 2.6.4 and older
              set_tunnel(self._proxy_host, self.port)
          else:
              set_tunnel(self._proxy_host, self.port, self.proxy_headers)
  
          conn.connect()
docs: Establish tunnel connection early, because otherwise httplib
          would improperly set Host: header to proxy's IP:port.