Dictionaries are ubiquitous in Python code; they are the data structure of choice for a wide variety of tasks. But dictionaries are mutable, which makes them problematic for sharing data in concurrent code. Python has added various concurrency features to the language over the last decade or so—async, free threading without the global interpreter lock (GIL), and independent subinterpreters—but users must work out their own solution for an immutable dictionary that can be safely shared by concurrent code. There are existing modules that could be used, but a recent proposal, PEP 814 ("Add frozendict built-in type"), looks to bring the feature to the language itself.