Linux.com :: Python 3.0 makes a big break
http://www.linux.com/feature/150399

"Developers hate it when a new version of a language doesn't work with the code written for older versions of that language, but for van Rossum, the radical upgrade was necessary. The language was becoming ever more weighed down by multiple ways of doing the same task, and ways of doing tasks no one ever actually did."

Typically, each new version of the Python programming language has been gentle on users, more or less maintaining backward compatibility with previous versions. But in 2000, when Python creator Guido van Rossum announced that he was embarking on a new version of Python, he did not sugar coat his plan: Version 3.0 would not be backward-compatible. Now that the first release candidate of Python 3.0 is out, with final release planned for later this month, developers must grapple with the issue of whether to maintain older code or modify it to use the new interpreter.