Python 2 is close to its end of life, and Google is starting to adjust its Python client libraries accordingly. Google AdWords/Ad Manager and Google Ads Python client libraries will soon require the use of at least Python 3.6+.
Python 2 is scheduled to deprecate sometime between mid-may to late-June of this year. Accordingly, in the last week of June, Google will release version 20.0.0 of the Google Ad manager API. This version will be incompatible with Python 2. On July 1, Google will end support for Python 2-related issues.
For developers desiring to use Python 2 as long as possible, don't migrate beyond version 19.0.0. Because v 20.0.0 will not support Python 2, the migration to Python 3 must occur before moving to Google's latest AdWords/Ad Manager and Ads clients. That being said, the Google Ads client library will continue compatibility with Python 2, via 19.0.0, until the end of 2019. However, starting July 1, Google will not prioritize Python 2 issues, and will likely only address major bugs for 19.0.0 after the July 1 date. Visit the developer blog for a more detailed timeline.