lru_cache with unhashable arguments

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lru_cache builds cache keys from the function arguments, and cache keys must be hashable (because they're stored as dict keys internally). Lists are mutable and unhashable, so passing a list raises TypeError: unhashable type: 'list'. The standard workaround is to convert the list to a tuple before calling the cached function: cached_fn(tuple(my_list)). This is a frequent gotcha when people try to memoize recursive functions that work on lists - you either restructure to pass tuples, or use a manual cache dict with custom key logic.