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Pass custom sys.paths to subprocess

  • these are research notes that could use a cleanup todo

when using python -m pip , certain paths that are added dynamically on blender startup, are ignored.
e.g. the appdata/roaming/.../addons path is not exposed to pip, since it’s dynamically added on Blender startup.

Print 
import site
site.getsitepackages()
['C:\\Program Files\\Blender Foundation\\Blender 3.2\\3.2\\python', 'C:\\Program Files\\Blender Foundation\\Blender 3.2\\3.2\\python\\lib\\site-packages']
site.getusersitepackages()
'C:\\Users\\user\\AppData\\Roaming\\Python\\Python310\\site-packages'

import sys
import pprint
pprint.pp(sys.path)
['C:\\Users\\user\\AppData\\Roaming\\Blender Foundation\\Blender\\3.2\\scripts\\modules',
'C:\\Program Files\\Blender Foundation\\Blender 3.2\\3.2\\scripts\\startup',
'C:\\Program Files\\Blender Foundation\\Blender 3.2\\3.2\\scripts\\modules',
'C:\\Program Files\\Blender Foundation\\Blender 3.2\\python310.zip',
'C:\\Program Files\\Blender Foundation\\Blender 3.2\\3.2\\python\\DLLs',
'C:\\Program Files\\Blender Foundation\\Blender 3.2\\3.2\\python\\lib',
'C:\\Program Files\\Blender Foundation\\Blender 3.2\\3.2\\python\\bin',
'C:\\Program Files\\Blender Foundation\\Blender 3.2\\3.2\\python',
'C:\\Program Files\\Blender Foundation\\Blender '
'3.2\\3.2\\python\\lib\\site-packages',
'C:\\Program Files\\Blender Foundation\\Blender 3.2\\3.2\\scripts\\freestyle\\modules',
'C:\\Program Files\\Blender Foundation\\Blender 3.2\\3.2\\scripts\\addons\\modules',
'C:\\Users\\user\\AppData\\Roaming\\Blender Foundation\\Blender\\3.2\\scripts\\addons\\modules',
'C:\\Program Files\\Blender Foundation\\Blender 3.2\\3.2\\scripts\\addons',
'C:\\Users\\user\\AppData\\Roaming\\Blender Foundation\\Blender\\3.2\\scripts\\addons',
'C:\\Program Files\\Blender Foundation\\Blender 3.2\\3.2\\scripts\\addons_contrib']

✅ pass env vars

we can’t pass the env, but we can pass PYTHONPATH or PATH
this worked. see PR

joined_paths = os.pathsep.join(sys.path)
env_var = os.environ.get("PYTHONPATH")
if env_var:
    os.environ["PYTHONPATH"] = f"{env_var}{os.pathsep}{joined_paths}"
else:
    os.environ["PYTHONPATH"] = joined_paths

The env var is auto passed to subprocess.run

❌ pass the env containing sys.paths

pass the ENV to the subprocess
passing the current env doesn’t work subprocess.run(command, env=os.environ.copy())

❔ .pth file

untested

pros

  • should fix the pip list issue not showing packages installed with --target
  • also will fix other issues e.g. with pip install upgrade

cons

  • adding a .pth file in program files/blender might need admin privilege
  • we have to manually recreate the env, instead of not worry about it and rely on blender for this
  • unsure if blender uses sitedir by default.

manually parsing env vars

CON

  • needs to be kept up to date. Blender is planning to change how user script paths work, so would need updating in future.

check what paths are, and if we can pass them as site dirs .

Blender Python Paths

if we pass the existing current env, we shouldn’t have to parse the following vars.

Blender

blender dir layout docs

use e.g. bpy.utils.resource_path('USER')
Search order: LOCAL, USER, SYSTEM. 
./scripts
./scripts/addons
./scripts/addons/modules
./scripts/addons_contrib
./scripts/addons_contrib/modules
./scripts/modules
./scripts/startup
./scripts/presets/{preset}
./scripts/templates_py

Search order: LOCAL, SYSTEM
./python

env vars docs

BLENDER_USER_RESOURCES
BLENDER_USER_SCRIPTS
BLENDER_SYSTEM_SCRIPTS
BLENDER_SYSTEM_PYTHON

script folder set in settings