my guess is copy paste error -- the original probably did not have the parens.
what version of python are you running on the mac?
are you using the console, or executing a file?
are you using jupyter or IPython or some other nonstandard interpreter?
The only other thought... since your class does not inherit from object, on 2.x this will be an "old style class", so might behave a little differently. But I think even old style classes would have bound instances to their methods.