Correct syntaxt to call object.draw_type = 'BOUNDS' as pie command? I would like to use bpy.context.object.draw_type = 'BOUNDS' as a pie operator like in the following line:

col.operator("object.draw_type", text="Object Solid", icon="MESH_CUBE").type='SOLID'


But I fail to figure out the correct way how to declare the type and get the error that draw_type has no attribute 'type' AttributeError: 'NoneType' object has no attribute 'type'.

I checked the API and do not find any clues about how to declare this directly inside an operator.


  Maximum draw type to display object with in viewport
  
  BOUNDS Bounds, Draw the bounds of the object. WIRE Wire, Draw the
  object as a wireframe. SOLID Solid, Draw the object as a solid (if
  solid drawing is enabled in the viewport). TEXTURED Textured, Draw the
  object with textures (if textures are enabled in the viewport).
  Type: enum in [‘BOUNDS’, ‘WIRE’, ‘SOLID’, ‘TEXTURED’], default
  ‘BOUNDS’
  
  draw_type Maximum draw type to display object with in viewport


Is this one of those commands where you have to define a class with the operator inside so you can all that via a pie instead?
read wm.py I promise this will be an eye-opener.

This has nothing to do with pies, pies are just specialized menu representations.  The property you are setting is an Enum ( a simple drop down in the UI is generally a representation of an Enum )

If you want to set the value of an Enum but don't want to present a dropdown, then you use wm.context_set_enum. 

    if context.active_object:
        obj = context.active_object
        set_draw_type = layout.operator("wm.context_set_enum", text="Object Solid", icon="MESH_CUBE")
        set_draw_type.data_path = "object.draw_type"
        set_draw_type.value = 'BOUNDS'


wm.context_set_enum is defined in the class WM_OT_context_set_enum, 
which delegated the execute function to execute_context_assign (also found in wm.py)