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5.7.4 Comparison to the built-in `set` types

The built-in `set` and `frozenset` types were designed based on lessons learned from the `sets` module. The key differences are:

- `Set` and `ImmutableSet` were renamed to `set` and `frozenset`.
- There is no equivalent to `BaseSet`. Instead, use `isinstance(x, (set, frozenset))`.
- The hash algorithm for the built-ins performs significantly better (fewer collisions) for most datasets.
- The built-in versions have more space efficient pickles.
- The built-in versions do not have a `union_update()` method. Instead, use the `update()` method which is equivalent.
- The built-in versions do not have a `_repr(sorted=True)` method. Instead, use the built-in `repr()` and `sorted()` functions: `repr(sorted(s))`.
- The built-in version does not have a protocol for automatic conversion to immutable. Many found this feature to be confusing and no one in the community reported having found real uses for it.