顺便学了下python的装饰器函数

装饰器原理:

其实就是把函数传到decorator中，然后将wrap函数返回给传进去的函数

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def a_new_decorator(a_func):
 
    def wrapTheFunction():
        print("I am doing some boring work before executing a_func()")
 
        a_func()
 
        print("I am doing some boring work after executing a_func()")
 
    return wrapTheFunction
 
def a_function_requiring_decoration():
    print("I am the function which needs some decoration to remove my foul smell")
 
a_function_requiring_decoration()
#outputs: "I am the function which needs some decoration to remove my foul smell"
 
a_function_requiring_decoration = a_new_decorator(a_function_requiring_decoration)
#now a_function_requiring_decoration is wrapped by wrapTheFunction()
 
a_function_requiring_decoration()

然后python提供了一个语法糖，可以将a_function_requiring_decoration = a_new_decorator(a_function_requiring_decoration)这句优雅地写成@a_new_decorator

代码如下，暂时只写了这些，以后会逐步完善。

先实例化一个类，然后这个类的实例替代requests，主要是用装饰器添加了异常捕获

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# 装饰器函数

def exceptDecoration(func):

  # 在这里添加self参数，可以使用类中的变量
  def wrapper(self, *args, **kwargs):
    retrieveCount = 0
    while(retrieveCount < 5):
      try:
        # 被装饰的函数
        response = func(self, *args, **kwargs)
        # 手动抛出HTTP异常
        response.raise_for_status()
        # 推测编码
        encoding = cchardet.detect(response.content)['encoding']
        response.encoding = encoding

        return response
      except requests.exceptions.HTTPError as err:
        print('错误码：%d\n%s' % (err.response.status_code))
        return err.response.status_code
      except requests.RequestException as err:
        delay = random.randrange(1, 4)
        print('%s\n延迟%d秒后重试 第%d次...' %
            (err, delay, retrieveCount))
        time.sleep(delay)
        print('重试...')
      finally:
        retrieveCount += 1

  return wrapper

class AskUrl():
  def __init__(self, *args, **kwargs):
    self.__args = args
    self.__kwargs = kwargs
    if 'headers' not in self.__kwargs:
      self.__kwargs['headers'] = {
        'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.25 Safari/537.36 Core/1.70.3775.400 QQBrowser/10.6.4208.400'
      }
    if 'method' not in self.__kwargs:
      self.__kwargs['method'] = 'GET'

    # 默认超时15秒
    if 'timeout' not in self.__kwargs:
      self.__kwargs['timeout'] = 20

    self.__session = None

  # 通过装饰器函数添加异常捕捉

  @exceptDecoration
  def request(self, *args, **kwargs):
    self.__updatePrams(*args, **kwargs)
    # 返回 在装饰器中用，元组和字典需要解一下传参
    return requests.request(*self.__args, **self.__kwargs)

  @exceptDecoration
  def session(self, *args, **kwargs):
    self.__updatePrams(*args, **kwargs)
    self.__session = requests.session()
    return self.__session.request(*self.__args, **self.__kwargs)

  def getSession(self):
    if not self.__session:
      print('必须先获得session对象')
      return None
    return self.__session

  # 此函数需要传入可变参数，不可直接传元组和字典
  def __updatePrams(self, *args, **kwargs):
    if(args):
      self.__args = (*self.__args, *args)
    if(kwargs):
      self.__kwargs.update(kwargs)

  def reset(self, *args, **kwargs):
    self.__args = args
    self.__kwargs = kwargs

askUrl = AskUrl()