RFC: Python Language Support (#2816)

Motion passed email: https://lists.osgeo.org/pipermail/grass-psc/2023-June/002726.html

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Co-authored-by: Markus Neteler <[email protected]>
Co-authored-by: Veronica Andreo <[email protected]>
Co-authored-by: Martin Landa <[email protected]>
Co-authored-by: Nicklas Larsson <[email protected]>
Co-authored-by: Vaclav Petras <[email protected]>

doc/development/rfc/python_language_support.md

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+# RFC 8: Python Language Support
+
+Authors: Nicklas Larsson
+
+Status: Adopted (5 June 2023)
+
+## Introduction
+
+The code base of GRASS GIS consists as of Feb. 2021 of predominantly C code
+(ca 50 %), Python (ca 30 %) and a smaller amount of C++ (ca 5 %). Each of these
+languages have evolved significantly in the last 10–20 years. There is, however,
+no clearly stated policy of supported language standard(s), nor mechanism to
+update this policy when needed or wanted. This result in uncertainty for
+contributors for what may be allowed and solutions that may not be optimal.
+
+This RFC aims at setting a policy for GRASS GIS project regarding the minimum
+version support for Python.
+
+## Background
+
+Similarly, the integration of Python within GRASS GIS – driving the GUI and
+to a large extent replacing shell scripts (bash/sh) for scripting – has gone
+through a challenging period with the transition from Python 2 to 3. This
+transition can now be considered completed, but this fact need to be formalised
+and the minimum version of Python 3 support must be stated.
+
+The minimum support for Python will, in contrast, likely change more often,
+due to each (minor) version’s 5-years life-time. At this date, the oldest
+still-alive Python version is 3.7, to be retired in June 2023.
+
+## Version Updates
+
+For a new release of a minor GRASS version, the Python minimum version should
+be raised in the [requirements](https://github.com/OSGeo/grass/blob/main/REQUIREMENTS.md#general-requirements)
+file if the current minimum Python version reaches end of life or there are any
+important technical reasons.
+
+At the same time, we raise the minimal Python version for a matching branch
+in grass-addons.
+
+For example, when Python 3.8 goes end-of-life before the release of 8.4.0, we
+raise the minimal Python version for 8.4.0 to 3.9. We also raise the minimal
+Python version for grass8 branch in grass-addons repo to Python 3.9.
+
+### References
+
+* Sunsetting Python 2: <https://www.python.org/doc/sunset-python-2/>
+* Active Python Releases: <https://www.python.org/downloads/>
+* Version list: <https://devguide.python.org/versions/>