Python 3 has full featured closures. In Python 2 it is not possible to alter what a variable references. It's still possible to alter the contents of the object

Python 3 has full featured closures. In Python 2 it is not possible to alter what a variable references. It's still possible to alter the contents of the object being referenced leading to the "put the value in a list" type of hackery to simulate full featured closures.