Where should I place the one-time operation operation in the Django framework?
We put one-time startup scripts in the top-level urls.py.  This is often where your admin bindings go -- they're one-time startup, also.
Some folks like to put these things in settings.py but that seems to conflate settings (which don't do much) with the rest of the site's code (which does stuff).
I want to perform some one-time operations such as to start a background thread and populate a cache every 30 minutes as initialize action when the Django server is started, so it will not block user from visiting the website. Where should I place all this code in Django?

Put them into the setting.py file does not work. It seems it will cause a circular dependency.
Put them into the __init__.py file does not work. Django server call it many times (What is the reason?)