Python's developers are strongly against the idea of invalidating old code with new releases, and have been historically very careful to ensure backwards compatibility with much older code. In 2005, the Python community had to deal with a difficult issue as reduce() and a number of other functions were removed from the standard library and had to be imported from another one as of Python 3000. In general, these things are announced and if your code stops running properly, the console provides helpful information that lets you find out why and make adjustments accordingly.