Python下HttpHTTPClient和AsyncHTTPClient

HTTPClient 使用例子：

    from tornado.httpclient import HTTPClient 
    
    def synchronous_fetch(url): 
　　　　　http_client = HTTPClient() 
　　　　　response = http_client.fetch(url) 
　　　　  return response.body

AsyncHTTPClient使用例子：

方法1：
    from tornado.httpclient import AsyncHTTPClient 

    def asynchronous_fetch(url, callback): 
　      http_client = AsyncHTTPClient() 
        def handle_response(response):     # 创建一个函数内的函数，来处理返回的结果
            callback(response.body) 
        http_client.fetch(url, callback=handle_response)   # 异步处理结束后会调用指定的callback的函数


方法2：
    from tornado.httpclient import AsyncHTTPClient 
    from tornado.concurrent import Future 

    def async_fetch_future(url): 
        http_client = AsyncHTTPClient() 
        my_future = Future() 
        fetch_future = http_client.fetch(url) 
        fetch_future.add_done_callback(lambda f: my_future.set_result(f.result())) 
        return my_future

方法3：
    from tornado.httpclient import AsyncHTTPClient 
    from tornado import gen 

    @gen.coroutine     #添加异步访问的装饰器
    def fetch_coroutine(url): 
        http_client = AsyncHTTPClient() 
        response = yield http_client.fetch(url)   # 获取异步结果时要使用yield 
        raise gen.Return(response.body)           # 使用抛出异常的方式来返回结果，不能使用return来返回


以下知识是额外的可以了解下，但不保证知识是完整的：
　　async and await  在python3.5，tornado4.3中可以了解下  
    
　　例子：
        async deffetch_coroutine(url): 
　　        http_client = AsyncHTTPClient()
            response = await http_client.fetch(url) 
            return response.body

    
使用yield来遍历异步的结果是，以下方法是在项目中没有试验过的
---------------------------------  start  --------------------------------------

@gen.coroutine
def parallel_fetch(url1, url2):
    resp1, resp2 = yield [http_client.fetch(url1),
                          http_client.fetch(url2)]

@gen.coroutine
def parallel_fetch_many(urls):
    responses = yield [http_client.fetch(url) for url in urls]
    # responses is a list of HTTPResponses in the same order

@gen.coroutine
def parallel_fetch_dict(urls):
    responses = yield {url: http_client.fetch(url)
                        for url in urls}
    # responses is a dict {url: HTTPResponse}

---------------------------------  end ----------------------------------------