I have a multi-file/multi-folder add-on, with preferences properties created in a prefs.py.

import bpy

class AddonPreferences(bpy.types.AddonPreferences):
    bl_idname = __package__

    my_property : bpy.props.BoolProperty(
        name = "my_bool",

I can easily access this bool in my __init__.py with:


But I can't manage to access it in panel.py placed in a UI folder. What is the correct way to call that property in a multi-file add-on?

  • $\begingroup$ I would guess those properties should be declared in a class, which is registered on blender startup? $\endgroup$
    – Rafal Zera
    Mar 16 '20 at 1:46
  • $\begingroup$ Yes I declare them in the init.py file: bpy.utils.register_class (prefs.AddonPreferences) But if I try to call them in my other files I get a KeyError: KeyError: 'bpy_prop_collection[key]: key "myaddon.ui.panel" not found' $\endgroup$
    – chafouin
    Mar 16 '20 at 2:01
  • $\begingroup$ @chafouin What is the value of __package__ in prefs.py? $\endgroup$
    – batFINGER
    Mar 16 '20 at 9:23
  • $\begingroup$ @batFINGER Is it something I have to define manually? $\endgroup$
    – chafouin
    Mar 17 '20 at 1:03
  • $\begingroup$ @batFINGER Printing it from the prefs.py returns the name of my top folder, which is the name of my addon (in that case, photographer) $\endgroup$
    – chafouin
    Mar 17 '20 at 3:51

My workaround was to have all the python files in a single folder and avoid subfolders. That way __package__ was returning the proper add-on name. This is not a real solution though.


I recently came across the same issue while developing an addon. I got a workaround from looking at this code of BlendLuxcore: use a mixture of basename and dirname from os.path to get to the folder name of your addon.


After observing how __init__.py packages everything together this simple trick worked. Please do let me know if some other correction is needed.

My folder structure:

The folder name (my_addon) should have pythonic name (no period, slash etc).

Now in __init__.py I put this simple import:

bl_info = {
    "name": "My addon",
    "version": (3, 0),
    "blender": (2, 90, 3),
    "category": "Sequencer",

# this (from . import) go up one folder 
#and will import the modules from that folder. 
#As a result will recognize as a package.

from . import somefunc, anotherfunc
from .somefolder import otherfunc

modules = (somefunc, anotherfunc, otherfunc)

def register():
    for m in modules:

def unregister():
    for m in modules:

if __name__ == "__main__":

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