def get_appapi_params(self, prepay_id, timestamp=None, nonce_str=None):
data = {<EOL>'<STR_LIT>': self.appid,<EOL>'<STR_LIT>': self.mch_id,<EOL>'<STR_LIT>': prepay_id,<EOL>'<STR_LIT>': '<STR_LIT>',<EOL>'<STR_LIT>': timestamp or to_text(int(time.time())),<EOL>'<STR_LIT>': nonce_str or random_string(<NUM_LIT:32>)<EOL>}<EOL>sign = calculate_signature(data, self._client.api_key)<EOL>data['<STR_LIT>'] = sign<EOL>return data<EOL>
获取 APP 支付参数

:param prepay_id: 统一下单接口返回的 prepay_id 参数值
:param timestamp: 可选，时间戳，默认为当前时间戳
:param nonce_str: 可选，随机字符串，默认自动生成
:return: 签名