o_18ufhmfmq19t513t3lgmn5l1qa8a.pdf

222 CHAPTER 10 ■ BATTERIES INCLUDED
Just as with dictionaries, the ordering of set elements is quite arbitrary, and shouldn’t be
relied on:
>>> set(['fee', 'fie', 'foe'])
set(['foe', 'fee', 'fie'])
In addition to checking for membership, you can perform various standard set operations
(which you may know from mathematics) such as union and intersection, either by using methods
or by using the same operations as you would for bit operations on integers (see Appendix B).
For example, you can find the union of two sets using either the union method of one of them
or the bitwise OR operator, |:
>>> a = set([1, 2, 3])
>>> b = set([2, 3, 4])
>>> a.union(b)
set([1, 2, 3, 4])
>>> a | b
set([1, 2, 3, 4])
Here are some other methods and their corresponding operators; the names should make
it clear what they mean:
>>> c = a & b
>>> c.issubset(a)
True
>>> c >> c.issuperset(a)
False
>>> c >= a
False
>>> a.intersection(b)
set([2, 3])
>>> a & b
set([2, 3])
>>> a.difference(b)
set([1])
>>> a - b
set([1])
>>> a.symmetric_difference(b)
set([1, 4])
>>> a ^ b
set([1, 4])
>>> a.copy()
set([1, 2, 3])
>>> a.copy() is a
False