Python – Contains of HashSet in Python

containshashsetpython

In Java we have HashSet<Integer>, I need similar structure in Python to use contains like below:

A = [1, 2, 3]
S = set()
S.add(2)
for x in A:
    if S.contains(x):
        print "Example"

Could you please help?

Best Answer

Just use a set:

>>> l = set()
>>> l.add(1)
>>> l.add(2)
>>> 1 in l
True
>>> 34 in l
False

The same works for lists:

>>> ll = [1,2,3]
>>> 2 in ll
True
>>> 23 in ll
False

Edit: Note @bholagabbar's comment below that the time complexity for in checks in lists and tuples is O(n) on average (see the python docs here), whereas for sets it is on average O(1) (worst case also O(n), but is very uncommon and might only happen if __hash__ is implemented poorly).