mat-assign-pie-menu.py

import bpy

bl_info = {
    "name": "FastMaterialAssign",
    "author": "Júlio Rodrigues",
    "version": (1, 0, 0),
    "blender": (2, 80, 0),
    "description": "Creates a Pie Menu for fast material assignment",
    "category": "Face",
}

# Creates a Pie Menu for fast material assignment

class AssignFaceMaterial(bpy.types.Operator):    
    bl_idname = "assign.material_pie_menu"
    bl_label = "Label Assign Material"
    bl_options = {'REGISTER', 'UNDO'}    

    active_index: bpy.props.IntProperty(name="Material Active Index in object's list")
    
    def execute(self, context):
        context.object.active_material_index = self.active_index
        bpy.ops.object.material_slot_assign()
        return {'FINISHED'}        

class VIEW3D_MT_Assign_Material(bpy.types.Menu):
    bl_label = "Assign Material"
    bl_id = "VIEW3D_MT_Assign_Material"

    def draw(self, context):
        layout = self.layout
        active_object = context.view_layer.objects.active        

        if active_object:
            mode = active_object.mode            
            if mode == "EDIT":       
                pie = layout.menu_pie()             
                for i, m in enumerate(context.object.data.materials):
                    props = pie.operator("assign.material_pie_menu", text=m.name, icon_value=m.preview.icon_id)
                    props.active_index = i
            

def register():    
    bpy.utils.register_class(AssignFaceMaterial)
    bpy.utils.register_class(VIEW3D_MT_Assign_Material)

def unregister():
    bpy.utils.unregister_class(AssignFaceMaterial)
    bpy.utils.unregister_class(VIEW3D_MT_Assign_Material)


if __name__ == "__main__":
    register()