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For windows you need to add onto the regedit

HKEY_CLASSES_ROOT > pytest

(Default) | REG_SZ | URL:pytest protocol

HKEY_CLASSES_ROOT > pytest > Shell > Open > Command

(Default) | REG_SZ | C:\Windows\py.exe -c "import os; import sys; from urllib.parse import unquote; args = sys argv[1:]; scrpath = unquote(args[0]).replace('pytest://', '')[:-1]; os.system('python '+scrpath)" "%L" %*

For linux idk.