addVariable doesn't properly support Domain subclasses

[WillDHB]

It seems like addVariable is intended to support using a subclass of Domain as a domain. However, this logic:

if hasattr(domain, "__getitem__"):
    domain = Domain(domain)
elif isinstance(domain, Domain):
    domain = copy.copy(domain)

will always convert to a Domain, since Domain objects implement __getitem__. It would appear that replacing it with this code would fix it:

if isinstance(domain, Domain):
    domain = copy.copy(domain)
elif hasattr(domain, "__getitem__"):
    domain = Domain(domain)

[scls19fr]

Hi @WillDHB

PR with tests are always welcome

Kind regards

[WillDHB]

Done. Sorry the code in the bug report was mangled; I didn't notice until just now.

[scls19fr]

To avoid code to be mangled, you just need triple backtick (see my edit)