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 ----------------------------------------
