"The previous article on Python version 3—also
known as Python 3000 or Py3K—discusses some of the basic
changes in Python that will break backwards compatibility, such as
the new print() function, the bytes data type, and changes to the
string type. This article, Part 2, explores some of the more
advanced topics, such as abstract base classes (ABCs), metaclasses,
function annotations and decorators, integer literal support, the
number type hierarchy, and changes to raising and catching
exceptions, most of which also break backwards compatibility with
the version 2x line.
"Class decorators
"In previous versions of Python, transformations to a method had
to be done after the definition of the method. In longer methods,
this requirement kept an important component of the definition far
removed from the definition of the external interface provided in
Python Enhancement Proposal (PEP) 318 (see Resources for a link).
This snippet shows an example of this transformation
requirement:"
