> How it should be handled? Currently PyUnicode_InternInPlace ignores any errors and does not return it. It would be backwards-incompatible to change that, moreover as I explained in https://github.com/python/cpython/pull/30683#discussion_r800648477 intern_strings only check if all the items are strings which will be always true in case of deep-freeze so I don't think anything needs to be changed here. I would be interested to know if I am missing something though.

The other functions you are calling *do* return errors. You should not ignore those. If any errors are reported the caller can decide what to do (e.g. call Py_FatalError().