Saying the parentheses are optional in Python 2 is kind of inaccurate. "print(thing)" is just "print (thing)", and "(thing)" is just an unnecessarily parenthesized version of "thing". So basically it's just redundant syntax that happens to make it look like a function.

If you try to do something like "print(thing1, thing2)" in Python 2, you'll find that "(thing1, thing2)" is interpreted as a tuple, so Python prints it as a tuple (instead of printing thing1 and thing2 individually).