What do new bpy class naming conventions in Blender 2.80 actually mean?

Question

What are the new class naming conventions in Blender's 2.80 Python API for add-ons?

It says here:

This constraint applies to the bl_idname of each class (or the class name which uses it if no bl_idname is defined in the class).

These are: UPPER_CASE_{SEPARATOR}_mixed_case, in the case of a menu the regular expression is:

[A-Z][A-Z0-9_]*_MT_[A-Za-z0-9_]+

The separator for each class is listed below:

• Header -> _HT_
  
• Menu -> _MT_
  
• Operator -> _OT_
  
• Panel -> _PT_
  
• UIList -> _UL_
  

Valid Examples:

• OBJECT_OT_fancy_tool
  
• SOME_HEADER_HT_my_header
  
• PANEL123_PT_myPanel (lower case is preferred but mixed case is supported).

At the time of writing this, names that don't conform to this convention will produce a warning on startup. Eventually we will make this into an error, eg:

Warning: 'Oscurart Files Tools' doesn't contain '_PT_' with prefix & suffix
Warning: 'Oscurart Overrides' doesn't contain '_PT_' with prefix & suffix
Warning: 'Oscurart Animation Tools' doesn't contain '_PT_' with prefix & suffix

So this might mean that the bl_idname should actually be something like:

"object.MY_ADDON_OT_some_object_operator"

It still requires a '.' to be there so object.OBJECT_OT_something_something does not seem to make much sense to me. Does this actually apply to bl_idname? Could someone explain in more detail the idea behind this and how these conventions should be followed in practice?

Answer 1

It seems bl_idname of operators is an exception to this new convention

Looking through Python scripts that come with Blender 2.80 I can see that the convention is followed in bl_idname and class name as described with:

• headers( _HT_ )
• menus( _MT_ )
• panels ( _PT_ )
• UI lists ( _UL_ )

but not with operators since that is not possible. Operators sometimes follow this convention in their class names, but never in bl_idname, where they follow the usual categorization with the dot, like bl_idname = "object.randomize_transform".

That was the confusing part to me since OBJECT_OT_fancy_tool was given as an example without clarification and it would definitely not work as a bl_idname for an operator.