select.select() 没有捕获套接字上的异常条件？
Python 2.7、Windows XP。我有一个向客户端发送消息的服务器。我使用 select 模块来检查套接字是否准备好接收，以及捕获异常情况。我的印象是，如果客户端关闭了套接字， select() 会在异常条件的套接字列表中返回所述套接字，但它似乎没有这样做：
lin, lout, lex = select.select(socklist, socklist, socklist)
for sock in lin:
# handle incoming messages
for sock in lout:
# send updates
for sock in lex:
# shut down server-side objects for particular client
What would be the best way for the server to certain客户端是否仍然连接？服务器并不总是发送数据，所以我不想依赖 socket.send() 来测试客户端是否仍然存在。
Python 2.7, Windows XP. I have a server that sends messages to client(s). I use select module to check for sockets ready to receive, as well as to catch exceptional conditions. I was under the impression that if a client closed a socket, select() would return said socket in the socket list of exceptional conditions, but it doesn't seem to be doing so:
lin, lout, lex = select.select(socklist, socklist, socklist)
for sock in lin:
# handle incoming messages
for sock in lout:
# send updates
for sock in lex:
# shut down server-side objects for particular client
What would be the best way for the server to determine whether the client is still connected? The server is not always sending data, so I would like not to have to rely on a socket.send() to test whether the client is still there.
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关闭的套接字不是异常（错误）情况。将会发生的情况是，套接字将位于读取列表 (lin) 中，并且当您读取时，您将获得 0 字节。这意味着另一端已关闭套接字。
更新：
在正常实践中，您永远不会在例外列表中看到任何内容，可以安全地忽略它。它适用于很少使用的东西，例如带外（OOB）等。
问题更新的答案：
可靠且快速地检测到套接字的另一端已消失可能很棘手。如果可靠、始终、及时地检测它很重要，那么您应该使用更高级别的机制，例如 keepalive/heartbeat。
如果客户端干净地关闭了套接字，那么您应该在读取列表中看到该套接字。从套接字读取将返回 0 字节，表示套接字已关闭 (EOF)。
A closed socket is not an exception (error) condition. What will happen is the socket will be in the read list (lin) and when you read you will get 0 bytes. This means the other end has closed the socket.
Update:
In normal practice you will never see anything in the except list and can safely ignore it. It is for rarely used things like out-of-band (OOB) and such.
Answer to question updates:
Reliably and quickly detecting that the other end of the socket has gone away can be tricky. If it's important to detect it reliably, always and in a timely fashion then you should use a higher level mechanism such as keepalive/heartbeat.
If the client does a clean shutdown of the socket, then you should see the socket in the read list. Reading from the socket will return 0 bytes which indicates the socket is closed (EOF).
套接字上“异常情况”的确切定义取决于底层实现。对于 Windows XP，底层实现是 WinSock 选择函数和异常条件包括：
The exact definition of "exceptional conditions" on a socket depends on the underlying implementation. For Windows XP, the underlying implementation is the WinSock select function and exceptional conditions include:
客户端关闭套接字也不例外。事实上，这绝不是例外。您将在异常情况列表中收到各种错误，但正确关闭的套接字不是其中之一。
A client closing a socket is not exceptional. It is in fact anything but exceptional. You will get various errors in the list of exceptional conditions, but a correctly closed socket is not one of them.