Tweaking the title to exclude servers. Persistent connections have apparently been supported in the low-level server for ages, since Issue 430706, and now that the close_connection flag is documented (Issue 23410), someone implementing a server should be able to use that to implement HTTP 1.0 keep-alive connections, etc as well.

For the client aspect, this bug is rather vague about exactly what should be added. Issue 3566 has been committed and closed, meaning now we should have an easier way to detect when a persistent connection has been dropped by the server. Here is a list of other things that come to mind:

1. Allow a way of polling for an unsolicited disconnection or 408 response without sending a request, either by:
  * exposing the sock attribute or adding a fileno() method, so that select() can be called, or
  * adding a new poll_response() or similar method
2. Poll if disconnected before sending a request, to avoid in 99% of cases the problem with non-idempotent requests (like POST) where you do not know if they were accepted or not
3. Change urlopen() to reuse the same connection when retrying a request (e.g. for redirects, authentication)
4. A urllib.request.PersistentConnectionHandler class or other urlopen() level API where the caller can reuse the same connection for multiple requests to the same host. Like HTTPConnection mainly does, but with the extra redirect, error, etc handling of urlopen().

I think the first point is important to do, because I have had to work around this by relying on the undocumented “HTTPConnection.sock” attribute. Once point 1 is done, point 2 might be easy to do in user code.

The last two points I currently don’t have so much personal interest in seeing in the standard library, unless others also want something like them.