Python Morsels: Practical uses of sets

Table of contents

1. What are sets?
2. Sets are like dictionaries without values
3. Quick containment checks with sets
4. Using set arithmetic
5. Converting to a set for efficiency
6. Checking for duplicates
7. What are sets good for in Python?

What are sets?

Like lists, sets are collections of values:

>>> fruits={"apples","strawberries","pears","apples"}

But unlike lists, sets can't contain duplicate values:

>>> fruits{'apples', 'pears', 'strawberries'}

And sets are also unordered, meaning the values within a set may move around as new items are added to the set:

>>> fruits.add("limes")>>> fruits{'apples', 'pears', 'lime', 'strawberries'}

Sets are like dictionaries without values

Have you ever found yourself …