Simplify single source

source/discussions/index.rst

@@ -16,3 +16,4 @@ specific topic. If you're just trying to get stuff done, see
    package-formats
    src-layout-vs-flat-layout
    setup-py-deprecated
+   single-source-version

source/discussions/single-source-version.rst

@@ -0,0 +1,47 @@
+.. _`Single sourcing the version`:
+
+===================================
+Single-sourcing the Project Version
+===================================
+
+:Page Status: Complete
+:Last Reviewed: 2024-??
+
+One of the challenges in building packages is that the version string can be required in multiple places.
+
+* It needs to be specified when building the package (e.g. in :file:`pyproject.toml`)
+   This will make it available in the installed package’s metadata, from where it will be accessible at runtime using ``importlib.metadata.version("distribution_name")``.
+
+* A package may set a top level ``__version__`` attribute to provide an alternative means of runtime access to the version of the imported package. If this is done, the value of ``__version__`` attribute and that used by the build system to set the distribution's version should be kept in sync in :ref:`the build systems's recommended way <Build system version handling>`.
+
+* If the code is in in a version control system (VCS), e.g. Git, the version may appear in a *tag* such as ``v1.2.3``.
+
+To ensure that version numbers do not get out of sync, it is recommended that there is a single source of truth for the version number.
+
+In general, the options are:
+
+1) If the code is in a version control system (VCS), e.g. Git, then the version can be extracted from the VCS.
+
+2) The version can be hard-coded into the :file:`pyproject.toml` file -- and the build system can copy it into other locations it may be required.
+
+3) The version string can be hard-coded into the source code -- either in a special purpose file, such as :file:`_version.txt`, or as a attribute in the :file:`__init__.py`, and the build system can extract it at build time.
+
+
+Consult your build system's documentation for their recommended method.
+
+.. _Build system version handling:
+
+Build System Version Handling
+-----------------------------
+
+The following are links to some build system's documentation for handling version strings.
+
+* `Flit <https://flit.pypa.io/en/stable/>`_
+
+* `Hatchling <https://hatch.pypa.io/1.9/version/>`_
+
+* `PDM <https://pdm-project.org/en/latest/reference/pep621/#__tabbed_1_2>`_
+
+* `Setuptools <https://setuptools.pypa.io/en/latest/userguide/distribution.html#specifying-your-project-s-version>`_
+
+  -  `setuptools_scm <https://setuptools-scm.readthedocs.io/en/latest/>`_