STL file too slow to load

Question

I'm new on Blender and I'm struggling with Blender's import operator for STL files. In my code, I try to load a file from the browser and then make some actions on the loaded object. I can get the file I want but the code continues to run before the STL file is loaded, so I get the error: KeyError: 'bpy_prop_collection[key]: key "file_name" not found'

Here's my code:

import bpy
from bpy_extras.io_utils import ImportHelper
from bpy_extras.io_utils import ExportHelper
from bpy.props import StringProperty, BoolProperty, EnumProperty
from bpy.types import Operator
#clearing previous objects
bpy.ops.object.select_all(action='SELECT')
bpy.ops.object.delete(use_global=False)
#stl file loading
bpy.ops.import_test.some_data('INVOKE_DEFAULT')
#some action with the file
x_dimension = bpy.data.objects["file_object"].dimensions[0]

Using :

class ImportSomeData(Operator, ImportHelper):
   """This appears in the tooltip of the operator and in the generated docs"""
   bl_idname = "import_test.some_data"
   bl_label = "Import Some Stl File"
   bl_options = {'REGISTER', 'UNDO'}
ImportHelper mixin class uses this
filename_ext = ".stl"
   filter_glob: bpy.props.StringProperty(
               default="*.stl",
               options={'HIDDEN'})
def execute(self, context):
       if self.filepath:
           bpy.ops.import_mesh.stl(filepath=self.filepath)
           # Print the imported object reference
           print ("Imported object:", context.object)
           # Create a material
           mat = bpy.data.materials.new(name="STLMaterial")
           # Append the material to the last slot
           context.object.data.materials.append(mat)
   return {'FINISHED'}

Only needed if you want to add into a dynamic menu
def menu_func_import(self, context):
   self.layout.operator(ImportSomeData.bl_idname, text="Text Import Operator")
def register():
   bpy.utils.register_class(ImportSomeData)
   bpy.types.TOPBAR_MT_file_import.append(menu_func_import)
def unregister():
   bpy.utils.unregister_class(ImportSomeData)
   bpy.types.TOPBAR_MT_file_import.remove(menu_func_import)
if name == "main":
   register()

Found on How to import a STL file using the file browser?.

Is there a way to stop the code until the STL file has loaded?

Thanks!