The PyTuple_SET_ITEM() and PyList_SET_ITEM() functions don't check that the index is valid. It should be checked with an assertion.

Linked PRs

• gh-106168: PyTuple_SET_ITEM() now checks the index #106164
• gh-106168: Check allocated instead of size index bounds in PyList_SET_ITEM() #111480
• gh-106168: Update PyList_SET_ITEM() What's New doc #111618
• gh-106168: Revert the "size before item" setting #111683