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.host, self.port)
        else:
            set_tunnel(self.host, self.port, self.proxy_headers)

        conn.connect()
Establish tunnel connection early, because otherwise httplib
dataset/ETHPy150Open kennethreitz/requests/requests/packages/urllib3/connectionpool.py/HTTPSConnectionPool._prepare_proxy