With the recent -- and long-awaited -- release of Debian 10 ("Buster"), there are no longer any "current" releases of commonly-used GNU/Linux desktop distributions that are shipping with Python 3.5: Ubuntu 18.04 LTS is shipping with Python 3.6, while every other popular distro (including Ubuntu 19.04, Debian 10, Fedora 29+, Slackware 14.2, ArchLinux) is shipping with Python 3.7. The number of users who both a) wish to build/install Gridsync from source and b) only have access to Python 3.5 is probably extremely small -- perhaps even non-existent, given that tools like pyenv make it quite easy to install newer python interpreters even on very old systems, while the recently-landed Vagrant/VirtualBox build-system reduces the need to rely on the local system interpreter entirely.

Requiring a minimum version of Python 3.6, furthermore, can provide several benefits to the Gridsync codebase: Python 3.6's support for literal string interpolation, for example, can significantly improve code-readability and conciseness, while support for variable type-annotations can (in conjunction with static type-checkers like mypy) help to detect and correct certain classes of type-related errors. It would be useful if the Gridsync project could begin to take advantage of these language-improvements now that Python 3.6+ is (finally) commonplace.