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What is the best practice way to store a python list defined in an addon as a scene variable in Blender?

Using

global mylist

doesn't work because the variable is not a Blender-specific type and therefore not saved after a button click operation completes. I would like the list to exist in the Blender environment so that I can access it from future function calls.

My current solution is to use Blender Collection Properties, with my own wrapper functions, but this seems kind of excessive:

bpy.types.Object.CP_list = bpy.props.CollectionProperty(type=bpy.types.PropertyGroup)

def CollectionProperty2list(CP, numerical = False):
    new_list = []
    if (numerical):
        for elt in CP:
            new_list.append(float(elt.name))
    else:
        for elt in CP:
            new_list.append(elt.name)
    return (new_list)

def list2CollectionProperty(mylist, CP):
    CP.clear()
    for elt in mylist:
        CP.add().name = str(elt)  # stores string for numerical or string input
    return()

storing:

list2CollectionProperty(py_list, obj.CP_list)

retreiving:

py_list = CollectionProperty2list(obj.CP_list)
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  • $\begingroup$ What seems more practical to me would be a way to store an entire python list to a single Blender variable, rather than assigning each element separately, and then retrieving each element separately. $\endgroup$
    – Animik
    Aug 11, 2017 at 16:48

1 Answer 1

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Storing a list as an ID property

# assign a list
>>> C.scene["mylist"] = [1, 1, 1, 1, 1, 1]
>>> C.scene['mylist']
<bpy id property array [6]>
# save file, reopen
>>> C.scene['mylist'].to_list()
[1, 1, 1, 1, 1, 1]

This will work for lists where all items are of the same type: strings, ints, floats or booleans (booleans as ints).

Could try using your methods above as getters / setters ... but I don't think get is available for bpy.props.CollectionProperty.

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    $\begingroup$ So simple! Also works for objects, without having to use the Blender properties: ob["mylist"] = py_list $\endgroup$
    – Animik
    Aug 18, 2017 at 13:43

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