https://peps.python.org/pep-0814/ adds a new `frozendict` builtin type. It's available for testing in Python 3.15 alpha 7: * https://docs.python.org/3.15/whatsnew/3.15.html#whatsnew315-frozendict ```console ❯ cat 1.py frozendict(x=1, y=2) ❯ ruff --version ruff 0.15.6 ❯ ruff check 1.py F821 Undefined name `frozendict` --> 1.py:1:1 | 1 | frozendict(x=1, y=2) | ^^^^^^^^^^ | Found 1 error. ``` Workaround for now, add to `pyproject.toml`: ```toml [tool.ruff] builtins = [ "frozendict" ] ```