older version of the computer programming language python begin with the version number 2 followed by dots and subversion numbers, such as

• python2.4
• python2.6
• python2.6.1

etc.

Python 3.0 is not 100% backward compatible with the python2.x versions. See History_of_Python. Some of the features of python3.x are backported to the newer versions of python 2.6.

During this book, all code examples are referring to python3.x if not written otherwise.