The final Python 3.5 release was 3.5.10 in September. This release series is now End-of-Life (EOL). The only LTS distribution that still only ships Python 3.5 is Ubuntu 16.04, which will be EOL in April 2021.
Python 3.6 has numerous features that we find useful such as improved support for the typing module, f-string support, and better integration with the pathlib module.
As a result, we will begin requiring Python 3.6 or newer in Meson 0.57, which is the next release. Starting with Meson 0.56, we now print a NOTICE: when a meson command is run on Python 3.5 to inform users about this. This notice has also been backported into the 0.55.2 stable release.