5.15.4 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:
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- Set and ImmutableSet were renamed to set and
- 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()
- 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.