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  • Asyncio

    2020-12-02 13:22:30
    <div><p>Working asyncio and aiohttp implementation, replacing the <code>requests</code> library (for talking to bitcoind's multiple RPC threads asynchronously). You should use python 3.4.1 or ...
  • asyncio

    2020-10-19 21:04:19
    asyncio是Python 3.4版本引入的标准库,直接内置了对异步IO的支持。 asyncio的编程模型就是一个消息循环。我们从asyncio模块中直接获取一个EventLoop的引用,然后把需要执行的协程扔到EventLoop中执行,就实现了异步...

    asyncioPython 3.4版本引入的标准库,直接内置了对异步IO的支持。

    asyncio的编程模型就是一个消息循环。我们从asyncio模块中直接获取一个EventLoop的引用,然后把需要执行的协程扔到EventLoop中执行,就实现了异步IO。

    asyncio实现Hello world代码如下:

    import asyncio
    
    @asyncio.coroutine
    def hello():
        print("Hello world!")
        # 异步调用asyncio.sleep(1):
        r = yield from asyncio.sleep(1)
        print("Hello again!")
    
    # 获取EventLoop:
    loop = asyncio.get_event_loop()
    # 执行coroutine
    loop.run_until_complete(hello())
    loop.close()
    

    @asyncio.coroutine把一个generator标记为coroutine类型,然后,我们就把这个coroutine扔到EventLoop中执行。

    hello()会首先打印出Hello world!,然后,yield from语法可以让我们方便地调用另一个generator。由于asyncio.sleep()也是一个coroutine,所以线程不会等待asyncio.sleep(),而是直接中断并执行下一个消息循环。当asyncio.sleep()返回时,线程就可以从yield from拿到返回值(此处是None),然后接着执行下一行语句。

    asyncio.sleep(1)看成是一个耗时1秒的IO操作,在此期间,主线程并未等待,而是去执行EventLoop中其他可以执行的coroutine了,因此可以实现并发执行。

    我们用Task封装两个coroutine试试:

    import threading
    import asyncio
    
    @asyncio.coroutine
    def hello():
        print('Hello world! (%s)' % threading.currentThread())
        yield from asyncio.sleep(1)
        print('Hello again! (%s)' % threading.currentThread())
    
    loop = asyncio.get_event_loop()
    tasks = [hello(), hello()]
    loop.run_until_complete(asyncio.wait(tasks))
    loop.close()
    

    观察执行过程:

    Hello world! (<_MainThread(MainThread, started 140735195337472)>)
    Hello world! (<_MainThread(MainThread, started 140735195337472)>)
    (暂停约1)
    Hello again! (<_MainThread(MainThread, started 140735195337472)>)
    Hello again! (<_MainThread(MainThread, started 140735195337472)>)
    

    由打印的当前线程名称可以看出,两个coroutine是由同一个线程并发执行的。

    如果把asyncio.sleep()换成真正的IO操作,则多个coroutine就可以由一个线程并发执行。

    我们用asyncio的异步网络连接来获取sina、sohu和163的网站首页:

    import asyncio
    
    @asyncio.coroutine
    def wget(host):
        print('wget %s...' % host)
        connect = asyncio.open_connection(host, 80)
        reader, writer = yield from connect
        header = 'GET / HTTP/1.0\r\nHost: %s\r\n\r\n' % host
        writer.write(header.encode('utf-8'))
        yield from writer.drain()
        while True:
            line = yield from reader.readline()
            if line == b'\r\n':
                break
            print('%s header > %s' % (host, line.decode('utf-8').rstrip()))
        # Ignore the body, close the socket
        writer.close()
    
    loop = asyncio.get_event_loop()
    tasks = [wget(host) for host in ['www.sina.com.cn', 'www.sohu.com', 'www.163.com']]
    loop.run_until_complete(asyncio.wait(tasks))
    loop.close()
    

    执行结果如下:

    wget www.sohu.com...
    wget www.sina.com.cn...
    wget www.163.com...
    (等待一段时间)
    (打印出sohu的header)
    www.sohu.com header > HTTP/1.1 200 OK
    www.sohu.com header > Content-Type: text/html
    ...
    (打印出sina的header)
    www.sina.com.cn header > HTTP/1.1 200 OK
    www.sina.com.cn header > Date: Wed, 20 May 2015 04:56:33 GMT
    ...
    (打印出163的header)
    www.163.com header > HTTP/1.0 302 Moved Temporarily
    www.163.com header > Server: Cdn Cache Server V2.0
    ...
    

    可见3个连接由一个线程通过coroutine并发完成。

    小结
    asyncio提供了完善的异步IO支持;

    异步操作需要在coroutine中通过yield from完成;

    多个coroutine可以封装成一组Task然后并发执行。

    参考源码
    async_hello.py

    async_wget.py

    展开全文
  • asyncio compatibility

    2020-12-02 14:11:29
    <div><p>Does pylogix have any asyncio compatibility? Not sure if this is a dumb question since I'm just learning about asyncio. Other libraries such as freeOpcUa have a specific library for ...
  • python asyncio asyncio wait

    2019-07-20 10:32:00
    import asyncio import time async def get_html(url): print("start get url") await asyncio.sleep(2) # 不能使用time.sleep(),这样的话是同步,就不是异步;await就相当于yield from print("end get url...
    import asyncio
    import time
    async def get_html(url):
        print("start get url")
        await asyncio.sleep(2) # 不能使用time.sleep(),这样的话是同步,就不是异步;await就相当于yield from
        print("end get url")
    
    if __name__ == "__main__":
        start_time = time.time()
        loop = asyncio.get_event_loop()
        tasks = [get_html("http://www.imooc.com") for i in range(10)]
      loop.run_until_complete(asyncio.wait(tasks)) #loop.run_until_complete将task放到loop中,进行事件循环, 这里必须传入的是一个list
    print(time.time()-start_time)

     

    转载于:https://www.cnblogs.com/callyblog/p/11216886.html

    展开全文

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