pytest ignores `-P` (avoid prepend) argument provided to Python

[Andrej730]

Python 3.11, Windows 11, pytest==8.2.2

1. Create new_test.py in your current folder.

   import sys
   print(sys.path)

2. Run py -P -m pytest new_test.py --capture=no

   C:\numpy> py -P -m pytest new_test.py --capture=no
   =============================================================================================================== test session starts ===============================================================================================================
   platform win32 -- Python 3.11.7, pytest-8.2.2, pluggy-1.5.0
   rootdir: C:\\numpy
   configfile: pytest.ini
   collecting ... ['C:\numpy', 'C:\numpy\\build-install\\usr\\Lib\\site-packages', 'Python311\\python311.zip', 'Python311\\DLLs', 'Python311\\Lib', 'Python311', 'Python311\\Lib\\site-packages', 'Python311\\Lib\\site-packages\\win32', 'Python311\\Lib\\site-packages\\win32\\lib', 'Python311\\Lib\\site-packages\\Pythonwin']
   collected 0 items

3. As you can notice C:\numpy is present in sys.path now, therefore import numpy will import numpy not from C:\numpy\\build-install\\usr\\Lib\\site-packages as it's set by PYTHONPATH environment variable but from C:\numpy which is not intended since -P is provided: https://github.com/numpy/numpy/issues/26816

Example of how -P option usually works

py -P new_test.py   
['C:\numpy\\build-install\\usr\\Lib\\site-packages', 'Python311\\python311.zip', 'Python311\\DLLs', 'Python311\\Lib', 'Python311', 'Python311\\Lib\\site-packages', 'Python311\\Lib\\site-packages\\win32', 'Python311\\Lib\\site-packages\\win32\\lib', 'Python311\\Lib\\site-packages\\Pythonwin']

[RonnyPfannschmidt]

The pytest import mode is independent from python and configured with a different option

In general its recommended to use the pytest - command to avoid python adding cwd to sys.path

[Andrej730]

The pytest import mode is independent from python and configured with a different option In general its recommended to use the pytest - command to avoid python adding cwd to sys.path

What would be the recommended way to avoid pytest adding cwd to sys.path?

[RonnyPfannschmidt]

See the pytest docs on import modes