Beginner python set intersection error

Question

rare = (["word1","word4","word5"])
freq = (["word1","word2","word3"])
unique = rare.intersection(freq)
print unique

error: AttributeError: 'list' object has no attribute 'intersection'

Am I not creating the sets correctly? They look like the examples in documentation -- but I can't seem to use normal set methods on them.

What is the proper syntax for creating sets if these are lists?

Answer 1

This way you're not creating sets, just regular lists. Use the set function:

rare = set(["word1","word4","word5"])
freq = set(["word1","word2","word3"])

Maybe you're confusing sets with tuples. A tuple is created with expressions between parenthesis, but you must provide at least a comma:

("this", "is", "a", "tuple")
("anotherone",)

Tuples are like immutable lists, but they're not sets.

Answer 2

On Python 2.7+, this is syntax for intersections using set operators:

>>> rare = {"word1", "word4", "word5"}
>>> freq = {"word1", "word2", "word3"}
>>> rare & freq
{'word1'}