PEP 796: Relative Virtual Environments #4476
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Co-authored-by: Alyssa Coghlan <[email protected]> Co-authored-by: Adam Turner <[email protected]> Co-authored-by: Stan Ulbrych <[email protected]>
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| @@ -1,22 +1,25 @@ | ||||||||
| PEP: 796 | ||||||||
| Title: Relative Home Path in Virtual Environments | ||||||||
| Author: Richard Levasseur <[email protected]> | ||||||||
| Sponsor: Alyssa Coghlan <[email protected]> | ||||||||
| Discussions-To: Pending | ||||||||
| Status: Draft | ||||||||
| Type: Standards Track | ||||||||
| Created: 02-Jul-2025 | ||||||||
| Python-Version: 3.15 | ||||||||
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| Abstract | ||||||||
| ======== | ||||||||
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| This PEP formally specifies the use of a relative path for ``home`` | ||||||||
| in a Python virtual environment's :file:`pyvenv.cfg` file. | ||||||||
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| Specifically, we will discuss how such relative paths are understood | ||||||||
| by the Python startup process, including their conversion to absolute | ||||||||
| paths for use by the runtime. | ||||||||
| This is a fundamental building block for virtual environments to | ||||||||
| become more portable. | ||||||||
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| Motivation | ||||||||
| ========== | ||||||||
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@@ -87,17 +90,19 @@ Specification | |||||||
| ============= | ||||||||
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| The ``home`` value in ``pyvenv.cfg`` is permitted to use a relative path value. | ||||||||
| These may contain parent-directory references outside of the virtual environment root | ||||||||
| directory. | ||||||||
| For example: | ||||||||
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| * ``subdir/whatever/bin`` (a directory within the virtual environment) | ||||||||
| * ``./subdir/whatever/bin`` (same as above) | ||||||||
| * ``../../../../../elsewhere/runtime/bin`` (a directory outside the virtual | ||||||||
| environment) | ||||||||
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| Relative paths are relative to the directory containing :file:`pyvenv.cfg`. | ||||||||
| During interpreter startup (i.e. :file:`getpath.py`), the relative path is joined to the | ||||||||
| directory containing ``pyvenv.cfg`` to form an absolute path. | ||||||||
| Parent-directory references (``../``) and current | ||||||||
| directory references (``./``) are resolved syntactically (i.e. not resolving | ||||||||
| symlinks). Symlinks are *not* resolved prior to construction of the absolute | ||||||||
| path to ensure semantics between a relative path and absolute path remain the | ||||||||
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@@ -110,7 +115,7 @@ i.e. it's equivalent to using that value verbatim in ``pyvenv.cfg``. | |||||||
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| CPython Runtime Changes | ||||||||
| ----------------------- | ||||||||
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| The CPython runtime itself *almost* already supports relative paths. The | ||||||||
| primitives are there, so the only change needed is to define how it resolves | ||||||||
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@@ -133,16 +138,15 @@ This change is only a couple of lines in the startup code. Specifically, when | |||||||
| parsing the ``pyvenv.cfg`` file and finding the ``home`` value, it just needs | ||||||||
| to be checked if it's already absolute. If not, then join it to the directory | ||||||||
| name of the ``pyvenv.cfg`` file. The code already knows the directory and has | ||||||||
| helpers already exist for checking if a path is absolute and joining two | ||||||||
| paths. | ||||||||
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| A proof-of-concept of this is implemented in the author's branch, | ||||||||
| `rickeylev/feat.relative.pyvenv.home <https://github.com/python/cpython/compare/main...rickeylev:cpython:feat.relative.pyvenv.home>`__. | ||||||||
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| `rickeylev/feat.relative.pyvenv.home <https://github.com/python/cpython/compare/main...rickeylev:cpython:feat.relative.pyvenv.home>`__. | |
| `rickeylev/feat.relative.pyvenv.home | |
| <https://github.com/python/cpython/compare/main...rickeylev:cpython:feat.relative.pyvenv.home>`__. |
Please could you also wrap some of the other long lines to 79 chars?
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(I don't mind if this isn't accepted, I've just always referred to this style of resolution as lexical rather than as syntactic: python/cpython#124825