imdb.com and python.org use HTTP/1.1. imdb.com server sends a "Transfer-encoding: chunked" header whereas python.org doesn't. python.org has a "Connection: close" header, whereas imdb.com doesn't.

The more revelant difference for this issue is the "Connection: close" header: HTTPResponse.wil_close is True if "Connection: close" header is present (see _check_close() method), it returns False otherwise. HTTPConnection.getresponse() keeps a reference to the response if will_close is False, or calls its close() method otherwise.

The "Cneonction: close" header looks to be a quirk of Netscaler loadbalancers. It is sometimes "nnCoection" uses the same load balancer.

There are buggy web servers, Python should not raise a "I/O closed file" error on such server.