KeyError: 'bpy_prop_collection[key]: key "View Layer" not found' when launching blender with external script

Question

When I execute the following code within Blender, it works well regardless of whether it's version 3.x or 4.x. However, if I try to use it by launching Blender with a specific argument to open a Blender file containing this script (e.g., blender --python myscript.py myfile.blend), the file opens correctly but the script triggers an error after Blender's addons load:

KeyError: 'bpy_prop_collection[key]: key "View Layer" not found'

I tried to override the context to force it to the Outliner, but encountered errors with that approach as well. Any thoughts?

import bpy
          
class ChrisMemoriserInvisible(bpy.types.Operator):
    bl_idname = "wm.memorise_invisible"
    bl_label = "Minimal Operator"
    
    @classmethod
    def description(cls, context, properties):
        return "get meshes and collection visibility"
        
    def execute(self, context):
        print("\n\r---- S T A R T I N G ---------------------\n\r")
        # Recursivly transverse collection
        def collections_recursively(collection):
            print(">>collection child: " + collection.name + " - invisible : " + str( collection.hide_viewport))
            if collection.hide_viewport == True:
                print("collection invisible :" + collection.name)
                f.write("collection>>" + collection.name +  "\r")
            for child in collection.children:
                collections_recursively(child)
       
        # Recursivly transverse layer_collection
        def recurLayerCollection(layerColl):
            found = None
            for layer in layerColl.children:
        #        print(">>>",layer.name)
                if layer.exclude == True:
                    print(layer.name,"true")
                    print("collection unchecked :" + layer.name)
                    f.write("layer>>" + layer.name +  "\r")
                elif layer.exclude == False:
                    print(layer.name,"false")
                    
                found = recurLayerCollection(layer)
                if found:
                    return found
         
        view_layer = bpy.context.scene.view_layers["View Layer"]
        obj_visibles = []
                
        with open("D:/_Chris/- SCRIPTS -/import_collection_invisible_mesh.ini","w") as f:              
            
            for o in bpy.context.scene.objects:
                if o.hide_get() == 0:
                    print ("visible : " + o.name)
                else:
                    print ("invisible : " + o.name )
                    f.write("mesh>>" + o.name +  "\r")  
               
                if o.hide_viewport == True:
                    print ("invisible : " + o.name )
                    f.write("meshview>>" + o.name +  "\r")  
                    
                    
            # collection with eye closed or not
            for collection in bpy.context.view_layer.layer_collection.children:
                print ("----------------------------------------")
                print(collection.name, ' - ', collection.hide_viewport)  
                collections_recursively(collection)  
                
            # collection unchecked or not
            for layer_collection in view_layer.layer_collection.children:
                if layer_collection.exclude == True:
                    print(layer_collection.name,"true")
                    print("collection unchecked :" + layer_collection.name)
                    f.write("layer>>" + layer_collection.name +  "\r")
                elif layer_collection.exclude == False:
                    print(layer_collection.name,"false")
                    
                layerColl = recurLayerCollection(layer_collection)
            
        f.closed    
        return {'FINISHED'} 

def register():
    bpy.utils.register_class(ChrisMemoriserInvisible)
   
def unregister():
    bpy.utils.unregister_class(ChrisMemoriserInvisible)   

if __name__ == "__main__":
    register()
    
    bpy.ops.wm.memorise_invisible()

UPDATE: the error I get from the console, the script I call is named cs_append_get_hidden_collections.py

Answer 1

Notice that the error appears before it reads the blend file. That is because your command should specify the blend file first and then the python script argument like this:

blender myfile.blend --python myscript.py

The issue arose because the command was structured with the --python script argument first, followed by the .blend file specification. In Blender's background mode, this sequence initially executes the Python script with a default setup where the view layer is named "ViewLayer" without a space. Consequently, the error occurs before Blender reads the .blend file specified. To resolve this, ensure that your command specifies the blend file first and then the Python script argument, like this:

blender myfile.blend --python myscript.py