[codebase] Python 3.6 required

design/003-codebase-python.md

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+# Proposal: Codebase - Python 3.6 required
+
+| **Status**        | **Accepted**                                    |
+|:------------------|:------------------------------------------------|
+| **RFC #**         | [003](https://github.com/conan-io/tribe/pull/3) |
+| **Submitted**     | 2020-11-20                                      |
+| **Tribe votes**   | :+1: (59)                                       |
+
+---
+
+## Summary
+Declare **Python 3.6** as the minimum Python version supported.
+
+
+## Motivation
+Python ecosystem is moving forward,
+[Python 3.5 has reached EOL](https://www.python.org/dev/peps/pep-0478/), and some
+core Conan dependencies will stop to support it, like
+[requests >2.25](https://requests.readthedocs.io/en/latest/community/updates/#id1).
+
+Python 3.6 has also [some valuable features](https://docs.python.org/3/whatsnew/3.6.html)
+that will help to improve the codebase and write more maintainable source:
+
+ * Formatted string literals a.k.a. _f-strings_.
+ * Type hints for classes and instance variables.
+
+
+## Proposal
+Python 3.6 will be the minimal supported version. Conan 2.0 is expected to be released
+on 2021, by that date Python 3.6 will be the oldest release alive (EOL on December 2021) and
+[Python 3.10 will be already released (October 2021)](https://www.python.org/dev/peps/pep-0619/).
+
+About Linux distros: starting on Debian 10 Buster (July 2019), the [Python 3
+version installed is Python 3.7](https://wiki.debian.org/Python). Ubuntu 18.04 (April 2018) already included Python 3.6.
+
+
+## Alternative Approaches
+Newer Python versions provide several enhancements on type annotation that could help
+to write and maintain code and some nice language features, but those are not _needed_
+and can block Conan 2.0 from being deployed on some wide-spread systems.
+
+
+## Detailed Design
+As soon as we include some f-string in the sources, the test suite will start to fail
+for any Python version older than 3.6.
+
+
+## Open issues
+Not known yet.
+
+
+## Future Extensions
+Not applicable.