def _prepare_conn(self, conn):
        """
        Prepare the ``connection`` for :meth:`urllib3.util.ssl_wrap_socket`
        and establish the tunnel if proxy is used.
        """

        if isinstance(conn, VerifiedHTTPSConnection):
            conn.set_cert(key_file=self.key_file,
                          cert_file=self.cert_file,
                          cert_reqs=self.cert_reqs,
                          ca_certs=self.ca_certs,
                          ca_cert_dir=self.ca_cert_dir,
                          assert_hostname=self.assert_hostname,
                          assert_fingerprint=self.assert_fingerprint)
            conn.ssl_version = self.ssl_version
        return conn

        Prepare the ``connection`` for :meth:`urllib3.util.ssl_wrap_socket`
        and establish the tunnel if proxy is used.
        
stackoverflow/venv/lib/python3.6/site-packages/pip-19.0.3-py3.6.egg/pip/_vendor/urllib3/connectionpool.py