gh-35403: Adopt the “time window-based” policy for support of Python …

…versions from Spec-0

    
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### 📚 Description

Add a short paragraph to the developer guide explaining the Python
support schedule. Previously discussed in #30384 and on the [mailing
list](https://groups.google.com/g/sage-devel/c/j1cwbTU8aOU). Closes
#30384.

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URL: #35403
Reported by: Tobias Diez
Reviewer(s): Dima Pasechnik

src/doc/en/developer/coding_basics.rst

@@ -82,6 +82,19 @@ In particular,
        def SomeIdentityValue(x):
            return SomeValue(1)
 
+.. _section-python-version:
+
+Python Version
+=================
+
+In order to reduce the technical debt of maintaining the project, Sage follows
+the time window-based support policy
+`SPEC 0 — Minimum Supported Dependencies <https://scientific-python.org/specs/spec-0000/>`_
+for Python versions. Accordingly, support for Python versions will be dropped 
+3 years after their initial release.
+For the drop schedule of Python versions, see the 
+`SPEC 0 <https://scientific-python.org/specs/spec-0000/#drop-schedule>`_
+document.
 
 .. _chapter-directory-structure: