I'm working on trying to run python under SerenityOS. At the moment, SerenityOS doesn't implement the TCP_NODELAY socket option. This makes the HTTPConnection.connect() method raise an OSError for an operation that is otherwise optional. Additionally, the connection object can be left in an intermediate state: the underlying socket is always created, but depending on what method was invoked (either connect() directly or a higher-level one such as putrequest()) the connection object can be in IDLE or REQ_STARTED state. I have a patch that works (attached), and I'll be working on submitting a PR now. Usage of TCP_NODELAY was introduced in 3.5 (#23302), so even though I've been testing against 3.10rc2 for the time being I'm sure it will affect all versions in between.