What word describes someone who isn't exactly optimistic, but has a positive outlook?

I need a word to describe someone who knows better than to expect the best, but can be happy in unfortunate circumstances.

I know phrases like "positive outlook" and "good disposition" could describe such a person, but I don't know any single words that would.

To differentiate between an optimist and the person I'm trying to describe:

When asking for a promotion, an optimist will expect to receive the promotion. The other person will hope for a promotion, but won't be disappointed without it.