June 26, 2019 Update
Python 2 End-Of-Life
On January 1st, 2020, Python 2 will reach the end of life. Since Python is the programming language used to write indexing pipeline extensions, starting September 3rd, all extensions written in Python 2 will need to be translated to Python 3, and customers will be required to write new extensions using Python 3.
However, you don’t need to handle the extension translation process yourself, unless you want to. The Coveo team will translate all customer Python 2 extensions to Python 3 and validate that the translations give the exact same results. You therefore don’t have anything to do, except use Python 3 to write new extensions after September 3rd, 2019.