Think Python, 3rd Edition

Chapter 18. Python Extras

One of my goals for this book has been to teach you as little Python as possible. When there were two ways to do something, I picked one and avoided mentioning the other. Or sometimes I put the second one into an exercise.

Now I want to go back for some of the good bits that got left behind. Python provides a number of features that are not really necessary—you can write good code without them—but with them you can write code that’s more concise, readable, or efficient, and sometimes all three.

Sets

Python provides a class called set that represents a collection of unique elements. To create an empty set, we can use the class object like a function:

s1 = set()
s1
       

set()
       

We can use the add method to add elements:

s1.add('a')
s1.add('b')
s1
       

{'a', 'b'}
       

Or we can pass any kind of sequence to set:

s2 = set('acd')
s2
       

{'a', 'c', 'd'}
       

An element can only appear once in a set. If you add an element that’s already there, it has no effect:

s1.add('a')
s1
       

{'a', 'b'}
       

Or if you create a set with a sequence that contains duplicates, the result contains only unique elements:

set('banana')
       

{'a', 'b', 'n'}
       

Some of the exercises in this book can be done concisely and efficiently with sets. For example, here is a solution to an exercise in Chapter 11 that uses a dictionary to check whether there are any duplicate elements in a sequence:

def has_duplicates(t):
    d = {}
    for x in t:
        d[x] = True
    return len(d) < len(t)
       

This version adds the element of t as ...