Upstream support for Python 2.7 is ending on January 1, 2020. Pallets is joining the community of open source projects ending support for Python 2 at that time. Our statement and support plan are based on PyTest's announcement.
We will be dropping support for Python 2.7 as well as Python 3.5 and below, as their support windows have ended or will end around the same time. Future releases of each Pallets project will only support Python versions still supported upstream, which can be found in the Python Developer's Guide.
The last version branch of each core project to support Python 2.7 and Python 3.5 are:
Each project will receive a major version bump to indicate support for only 3.6+:
Thanks to the python_requires package metadata, Python 2.7 and
3.5 users with a modern pip version will install the last supported
version automatically even if later versions are available.
The team will no longer backport patches for unsupported versions, but the branches will continue to exist. The team will be happy to accept patches contributed by the community for any severe security and usability issues until mid-2020.
We made this decision based on multiple factors. Foremost is ease of community contribution and maintainer availability. As time goes on, fewer contributors have used or are familiar with the differences between Python 2 and 3. Contributors and maintainers must keep track of an ever growing list of obscure compatibility issues and workarounds, and cannot use many modern features.
Over the last two years, we've talked to many developers and teams at conferences and meetups and heard overwhelming support for the move to Python 3. This is backed up by data collected from our community in a survey we ran during January 2019, with 92% of respondents already using or actively upgrading to Python 3. The PSF developer survey and PyPI statistics report similar majorities and show adoption continuing to increase.
Thank you to everyone in the community for your support, and to everyone who has made this transition a reality. We look forward to continuing to develop the Pallets projects with you!