Recent macOS breaks access to (documented) environment variables

[gav451]

Bug report

Bug description:

On recent versions of macOS user defined environment variables (also those documented at https://docs.python.org/3/using/cmdline.html#environment-variables like PYTHONHOME) are not known in Python on recent versions of macOS (I have tested it on Tahoe 26.2 where they are not known and Big Sur 11.7.1 where they are known). For instance after setting
PYTHONPLATLIBDIR=lib
in the shell and typing in a Python interpreter

import os
os.getenv("PYTHONPLATLIBDIR")

returns an empty string on recent versions of macOS.

CPython versions tested on:

3.14, 3.9

Operating systems tested on:

macOS

[ronaldoussoren]

This appears to work just fine:

% PYTHONPLATLIBDIR=lib python3.14                                                                       (main)pyobjc-12
Python 3.14.2 free-threading build (v3.14.2:df793163d58, Dec  5 2025, 12:31:15) [Clang 16.0.0 (clang-1600.0.26.6)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.getenv("PYTHONPLATLIBDIR")
'lib'
>>> 
>>> 

% sw_vers
ProductName:		macOS
ProductVersion:		26.2
BuildVersion:		25C56

Dit you "export" the environment variable? By default the shell does not export newly set variables to commands started from the shell.

[gav451]

Yes, it works after writing export PYTHONPLATLIBDIR=lib in my .zshenv or .zshrc instead of simply PYTHONPLATLIBDIR=lib which does not work.