Quote - So what is builtin all about?

It's a special module that contains all the methods supplied by the Python core.
When a script get executed, the environment that gets passed to it only contains the set of modules/methods etc. that the calling code has included in it.
I don't know yet whether the very minimal environment that the link scripts are running in is intentional or a bug (caused by an oversight, a change in Python internals, or something else).

The standard Python documentation will tell you what other functions will unavailable without importing builtin