Helper function to get the total number of classes for the detection task

def get_num_classes(pbtxt_fname):
from object_detection.utils import label_map_util
label_map = label_map_util.load_labelmap(pbtxt_fname)
categories = label_map_util.convert_label_map_to_categories(
label_map, max_num_classes=90, use_display_name=True)
category_index = label_map_util.create_category_index(categories)
return len(category_index.keys())

I can't import label_map_util but the folder object detetion and utils is exist
the error :
Import "object_detection.utils" could not be resolved(reportMissingImports)