CFEP: Unixy layout for python on windows

cfep-xx.md

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+<table>
+<tr><td> Title </td><td> A more unixy layout for cpython on windows </td>
+<tr><td> Status </td><td> Proposed </td></tr>
+<tr><td> Author(s) </td><td> Isuru Fernando &lt;ifernando@openteams.com&gt;</td></tr>
+<tr><td> Created </td><td> May 14, 2026</td></tr>
+<tr><td> Updated </td><td> May 14, 2026</td></tr>
+<tr><td> Discussion </td><td> https://github.com/conda-forge/python-feedstock/issues/860 </td></tr>
+<tr><td> Implementation </td><td> NA </td></tr>
+</table>
+
+## Abstract
+
+A more unixy layout for cpython package and downstreams on windows
+is proposed changing the places where python headers, libraries,
+site-packages and stdlib are placed. This proposal is for upcoming
+python 3.15 release and is not intended to be backported to older
+python releases.
+
+## Motivation
+
+Currently, the package layout for all conda packages
+are dictated by the python package. All C/C++ libraries, header
+files end up in <CONDA_PREFIX>/Library because <CONDA_PREFIX> is
+reserved for python due to its peculiarities on windows.
+See [CEP 0034](https://github.com/conda/ceps/blob/main/cep-0034.md#windows)
+for more details on the file system.
+This CFEP proposes changing this so that other libraries can use
+<CONDA_PREFIX>/lib, <CONDA_PREFIX>/include if they choose to.
+
+## Specification
+
+| Component            | Current           | Proposed                 | Unix reference                 | 
+| -------------------- | ----------------- | ------------------------ | ------------------------------ |
+| purelib/platlib      | Lib/site-packages | lib/python/site-packages | lib/python3.15t/site-packages  |
+| scripts              | Scripts           | Scripts                  | bin                            |
+| stdlib/platstdlib    | Lib               | lib/python               | lib/python3.15t                |
+| include/platinclude  | include           | include/python           | include/python3.15t            |
+| dynload              | DLLs              | lib/python/lib-dynload   | lib/python3.15t/lib-dynload    |
+| import libraries     | lib               | lib                      | lib                            |
+| sys.executable       | python.exe        | python.exe               | bin/python                     |
+
+## Implementation
+
+### python package support
+
+We propose implementing this CFEP for CPython 3.15 and up.
+This can be implemented by adding a `nt_conda` install scheme to [sysconfig](
+https://github.com/python/cpython/blob/v3.15.0b1/Lib/sysconfig/__init__.py#L28-L60)
+and then making it the default.
+
+See [debian patch](https://salsa.debian.org/cpython-team/python3/-/blob/python3.14/debian/patches/sysconfig-debian-schemes.diff?ref_type=heads) to see how they override the scheme to
+make the distinction between `dist-packages` (apt installed python packages)
+and `site-packages` (pip installed python packages).
+
+### conda support
+
+conda clients are only concerned with the location of the `scripts` and
+`purelib`/`platlib` components. The former needs to be added to `PATH`
+and both are needed for placing files in the correct layout for
+`noarch: python` packages. The others (`stdlib/platstdlib`, `platlibdir`
+and `include/platinclude`) can be changed without breaking anything.
+
+1. purelib/platlib
+
+   For this case we have `python_site_packages_path` and therefore all conda
+   clients support this.
+
+2. scripts
+
+   We are intentionally not changing the layout here because there's no way to
+   tell conda to install things here for `noarch: python` packages.
+   I propose adding a `python_scripts_path` as a CEP and use that in a future
+   release, but is out of scope for this CFEP.
+
+## Rationale for locations
+
+1. purelib/platlib
+
+   This matches unix, but removes the version and ABI flags. This is done to
+   have a version neutral location like it is in current windows layout.
+   Note: the author would also like to change the unix reference to match
+   the proposed windows layout, but is out-of-scope for this CFEP.
+
+2. scripts
+
+   No change because of conda limitation. See the previous section.
+
+3. stdlib/platstdlib
+
+   Same rationale as purelib/platlib
+
+4. include/platinclude
+
+   Same rationale as purelib/platlib
+
+5. dynload
+
+   These are internal places where `.pyd` and `py.ico` are installed and is
+   internal to cpython package. The directory `DLLs` does not interfere with any
+   other package, so we propose use the same directory as unix.
+
+## Copyright
+
+All CFEPs are explicitly [CC0 1.0 Universal](https://creativecommons.org/publicdomain/zero/1.0/).