Is there a way to retain an Add-On's preferences when updating the Add-on?

Question

I have a couple of preference properties (string, boolean, float) in my add-on and they all have a default value in their defining statement.

When I install an update to my add-on, the previously modified settings are not saved and the default values are used instead.

Is there a way to save the settings before the update and restore them afterwards? Or do I have to get rid of the default values from the properties? (That would be not so good.)

I was looking at the application handlers but I could not find a handler for add-on updates.

Does anyone have a best practice method for dealing with add-on preferences? Thanks in advance.

Update: here is how my add-on settings are defined:

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

    pref_library_path: bpy.props.StringProperty(name="pref_library_path",subtype="DIR_PATH", description = '...', default=Library_Location)
    pref_local_lib_path: bpy.props.StringProperty(name="pref_local_lib_path",subtype="DIR_PATH",description = '...', default="")
    pref_stage_height: bpy.props.FloatProperty(name ='pref_stage_height', description = '...', default=(240), soft_min=0, soft_max=1000)

Answer 1

I faced the same problem working on addon of mine, and the solution was to save them in a .env.

1. Download dotenv using pip install python-dotenv

2. Create a .env file in you addon main directory and add the default preferences to it.

3. Read the .env file using dotenv, like this:

    from dotenv import load_dotenv, find_dotenv
   
    dotenv_file = find_dotenv()
    load_dotenv(dotenv_file)
   

4. You can now retrieve any value from the .env using:

    from dotenv import dotenv_values, find_dotenv
    dotenv_file = find_dotenv()
    config = dotenv_values(dotenv_file)
    return config["YOUR_PREFERENCE_KEY"]
   

5. If you want to override the setting you can use the set_key function like this:

    from dotenv import set_key, find_dotenv
   
    dotenv_file = find_dotenv()
    set_key(dotenv_file, "YOUR_PREFERENCE_KEY", "YOUR_PREFERENCE_VALUE")
   

Hope this helps. Just make sure the user's .env doesn't get replaced with the stock one when updating.