5.7.4 Comparison to the built-in set types

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.

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