Python 3 is not backwards compatible with Python 2, so your code may need to be adapted.

Please start migrating your existing your existing Python 2 code to Python 3.

Python 2 series End Of Life is set to 1st of January 2020.

Introduction

Python 2.7 was released on July 2010. Being the last of the 2.x series, 2.7 has had an extended period of maintenance. Specifically, 2.7 will receive bugfix support until January 1, 2020. After the last release, 2.7 will receive no support. 

Python 3.0 was released on December 2008. It was designed to rectify fundamental design flaws in the language. The changes required break backwards compatibility with the 2.x series, which necessitated a new major version number.

Major changes

Subsequent releases in the Python 3.x series have included additional, substantial new features; all ongoing development of the language is done in the 3.x series.

Porting your code to python 3

For a complete reference and advise, see https://docs.python.org/3/howto/pyporting.html

It is possible to write code that works for both major versions of Python, and it is the recommended strategy for maximum compatibility and flexibility. See the following page for a comprehensive list of compatible idioms. The easiest way to make sure your python 2 code can run on python 3 is to use automatic conversion tools such as futurize. Even if they are not perfect in all cases, they should take care of adapting the vast majority of your code base without too many bugs introduced. Futurize will also generate code that is compatible with both editions. See the quick start guide for instructions on how to use this tool.

ECMWF software packages and libraries

Newest versions of the ECMWF packages and libraries support now both python 2 and 3. At ECMWF, their installations are done so both python 2.7 and 3.6 can be used.