Actually, because of issue 18543, urlopen will not use the custom opener if one was defined, instead, it will create a new opener with check_hostname = True.

So it is impossible to skip hostname checking without overriding the urlopen method.

I don't understand why can't we allow check_hostmane to be set to False in urlopen and also why we don't allow custom openers to be used by urlopen if specifying a ca*.

Moreover this forced restriction is not documented. I had to go to the source code to figure out why it wasn't working.

This issue being resolved makes it even more misleading.