how to fix "xxx attempted to use a functionality that requires module xxx, but it couldn't be loaded. Please install xxx and retry."

[happysheep224]

ImportError: mmskeleton.utils.third_party attempted to use a functionality that requires module mmdet.apis, but it couldn't be loaded. Please install mmdet and retry.

[thiswillbeyourgithub]

Same with "from datetime import datetime". Neither lazy_module nor lazy_callable worked