David Mertz - Picking a Python Version: A Manifesto

by David Mertz

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There are two major versions of the Python programming language: thePython 2.x series, and the newer Python 3.x series. The Python 3.x seriesstarted with the release of Python 3.0 in December 2008; since thattime, Python 2.7 was released and has continued to receive point versionreleases, with Python 2.7.9 being the latest version as of this writing.As a footnote, there was, naturally, a Python 1.x series that washighly successful in the 1990s, but that series has long beenout-of-maintenance.

In his 2014 PyCon keynote (), Guido van Rossum, Pythons Benevolent Dictator for Life (sometimes affectionately called the BDFL or GvR) made it clear that the Python 2.x series will not continue past Python 2.7.x. The end-of-life for Python 2.7.x is 2020, and no new features will be added to the 2.x series of Python.

Within a series, Python places an especially strong philosophicalemphasis on backward compatibility (in comparison to many otherprogramming languages). It is extremely rare for a series to breakthis backward compatibility in later minor versions; in the few caseswhere it has occurred, it is only to address large previouslyundiscovered bugs or security issues, and even then great attention ispaid to affecting as little running code as possible. That said, newPython versions inevitably add important features, either in thelanguage itself, its built-in functions, or in standard library supportmodules.

Figure 1-1. Guido van Rossums PyCon 2014 keynote address (photo credit: David Lesieur 2014, CC-BY-SA)

Python developers have numerous versions and implementations to choosefrom. Many of us still use Python 2.x and CPythonand that is still often agood choicebut there are many situations in which making adifferent choice makes sense.

Python 3.x, and in particular the Python 3.5 version coming out soon, offernumerous advantages over the Python 2.x series. New development should typicallybe done using Python 3.x, and although the 2020 end-of-life for Python 2.x isnt allthat close, it is good for companies and projects to start think ofporting plans for existing code.