Core Python Programming (2nd Edition)

7.9. Set Type Built-in Methods
7.9.1. Methods (All Set Types)
We have seen the operator equivalents to most of the built-in methods, summarized in Table 7.4.
Method Name Operation
Table 7.4. Set Type Methods
s.issubset(t) Returns TRue if every member of s is in t, False otherwise
s.issuperset(t) Returns true if every member of s is in t, False otherwise
s.union(t) Returns a new set with the members of s or t
s.intersection(t) Returns a new set with members of s and t
s.difference(t) Returns a new set with members of s but not t
s.symmetric_difference(t) Returns a new set with members of s or t but not both
s.copy() Returns a new set that is a (shallow) copy of s
The one method without an operator equivalent is copy(). Like the dictionary method of the same name,
it is faster to create a copy of the object using copy() than it is using a factory function like set(),
frozenset(), or dict().
7.9.2. Methods (Mutable Sets Only)
Table 7.5 summarizes all of the built-in methods that only apply to mutable sets, and similar to the
methods above, we have already seen most of their operator equivalents.
Method Name Operation
Table 7.5. Mutable Set Type Methods
s.update(t) Updates s with elements added from t; in other words, s now has
members of either s or t
s.intersection_update(t) Updates s with members of both s and t
s.difference_update(t) Updates s with members of s without elements of t