This is really IronPython 101 but this was a really difficult thing to find by Googling! There are also examples in IronPython in Action but again, searching for them if you're not sure what you're searching for won't get you very far. The solution is pretty similar to how you would do it in C:

>>>print "The opportunity '[%i] %s' has now expired" % (1, "Job 1")
The opportunity '[1] Job 1' has now expired