调用第三方服务API的SDK编写思路（手机话费充值SDK编写例子 ）

思路
通过将SDK方法中返回的数据划分为正常返回数据以及错误返回的数据两部分，让调用者更简单的对接口调用错误进行处理。
将SDK调用第三方服务接口的流程划分为: 数据准备，http请求，结果处理三部分，以重用代码。
例子
以聚合数据手机话费充值SDK编写为例, 手机话费充值API

# encoding=utf-8
from urlparse import urljoin
from hashlib import md5
from datetime import datetime
from random import sample
import requests
import pytz


class APIError(object):
    def __init__(self, code, msg):
        self.code = code
        self.message = msg


class JuhePhoneChargeApi(object):

    API_PREFIX = 'https://op.juhe.cn/ofpay/mobile/'
    def __init__(self, openid, key, api_entry=None):
        self._key = key
        self._openid = openid
        self._api_entry = api_entry or self.API_PREFIX


    def telcheck(self, phoneno, cardnum):
        params = {'phoneno': phoneno, 'cardnum': cardnum}
        return self._get(path='telcheck', params=params)

    def telquery(self, phoneno, cardnum):
        params = {
            'phoneno': phoneno,
            'cardnum': cardnum,
        }
        return self._get(path='telquery', params=params)

    def onlineorder(self, phoneno, cardnum, orderid):
        params = {
            'phoneno': phoneno,
            'cardnum': cardnum,
            'orderid': orderid or self.create_orderid(),
        }
        params.update({'sign': self._create_sign(**params)})

        return self._get(path='onlineorder', params=params)

    def ordersta(self, orderid):
        params = {'orderid': orderid}
        return self._get(path='orderid', params=params)

    def create_orderid(self):
        return ''.join((
            datetime.now(tz=pytz.timezone('Asia/Shanghai')).strftime('%Y%m%d%H%M%S%f'),
            self._create_code(12)))

    def _process_response(self, rsp):
        """
        对第三方接口返回数据做同一处理,
        :param rsp:
        :return:  接口正常返回值, 错误对象
        """
        if rsp.status_code != 200:
            return None, APIError(rsp.status_code, 'http error')
        try:
            content = rsp.json()
        except:
            return None, APIError(99999, 'invalid rsp')
        if 'error_code' in content and content['error_code'] != 0:
            return None, APIError(content['error_code'], content['reason'])

        return content['result'], None


    def _get(self, path, params=None):
        if not params:
            params = {}

        headers = {'Content-type': 'application/json'}
        params.update({'key': self._key})

        rsp = requests.get(urljoin(self._api_entry, path), params=params, headers=headers)
        return self._process_response(rsp)


    def _create_sign(self, phoneno, cardnum, orderid=None):
        obj_str = ''.join((
            self._openid, 
            self._key, 
            phoneno, 
            str(cardnum), 
            orderid or self.create_orderid()))

        m = md5()
        m.update(obj_str)
        return m.hexdigest()

    def _create_code(self, number_len):
        ELEMENT = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'
        return ''.join(sample(ELEMENT, number_len))