Advanced Python · Week 4

Sets

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Exercise 1: Introduction to Sets

Welcome to Python 2, Lesson 4! Today, we'll learn about sets, another useful data structure in Python.

What is a Set?

A set is an unordered collection of unique elements. This means that each item in a set appears only once, and the order doesn't matter.

Here's how to create a simple set:

# Create a set of fruits
fruits = {"apple", "banana", "cherry"}

print(fruits)
print(type(fruits))
            

Now it's your turn! Create a set called colors with the following items:

red
green
blue
red (yes, add it twice!)

After creating the set, print it and its type to see the result. Notice how duplicates are automatically removed!

Starter code

# Create the colors set here

# Print the set and its type

Write your code here

Exercise 2: Adding and Removing Elements

Now that we've created a set, let's learn how to add and remove elements.

Set Methods

add(item): Adds an item to the set
remove(item): Removes an item from the set (raises an error if the item is not found)
discard(item): Removes an item if it's present (does not raise an error if the item is not found)

Here's an example:

fruits = {"apple", "banana", "cherry"}

fruits.add("orange")
print(fruits)

fruits.remove("banana")
print(fruits)

fruits.discard("grape")  # This won't raise an error
print(fruits)
            

Your turn! Using the colors set from the previous exercise:

Add "yellow" to the set
Remove "green" from the set
Try to discard "purple" (which isn't in the set)
Print the set after each operation

Starter code

colors = {'red', 'green', 'blue'}

# Your code here

Write your code here

Exercise 3: Set Operations

Sets in Python support various mathematical operations that are very useful in programming.

Common Set Operations

union() or |: Combines elements from both sets
intersection() or &: Returns elements common to both sets
difference() or -: Returns elements in one set but not in the other
symmetric_difference() or ^: Returns elements in either set, but not in both

Here's an example:

set1 = {1, 2, 3, 4, 5}
set2 = {4, 5, 6, 7, 8}

print("Union:", set1 | set2)
print("Intersection:", set1 & set2)
print("Difference (set1 - set2):", set1 - set2)
print("Symmetric Difference:", set1 ^ set2)
            

Your task:

Create two sets: fruits1 with "apple", "banana", "cherry" and fruits2 with "banana", "orange", "kiwi"
Find and print the union of the two sets
Find and print the intersection of the two sets
Find and print the difference of fruits1 and fruits2
Find and print the symmetric difference of the two sets

Starter code

# Create the two fruit sets and perform set operations

Write your code here

Exercise 4: Sets vs Lists and Tuples

Now that we've learned about sets, let's compare them with lists and tuples to understand when to use each.

Sets vs Lists and Tuples

Sets are unordered; lists and tuples maintain order
Sets contain only unique elements; lists and tuples can have duplicates
Sets are mutable (can be changed) like lists, but their elements must be immutable
Sets are faster for checking if an item is present

Here's an example showing some differences:

# List
numbers_list = [1, 2, 2, 3, 4, 4, 5]
print("List:", numbers_list)

# Tuple
numbers_tuple = (1, 2, 2, 3, 4, 4, 5)
print("Tuple:", numbers_tuple)

# Set
numbers_set = {1, 2, 2, 3, 4, 4, 5}
print("Set:", numbers_set)

# Check if 3 is in each collection
print("Is 3 in list?", 3 in numbers_list)
print("Is 3 in tuple?", 3 in numbers_tuple)
print("Is 3 in set?", 3 in numbers_set)
            

Your task:

Create a list called fruits_list with "apple", "banana", "cherry", "apple", "date"
Create a tuple called fruits_tuple with the same elements as the list
Create a set called fruits_set from the list
Print all three and observe the differences
Check if "banana" is in each collection and print the results

Starter code

# Create a list, tuple, and set of fruits, then compare them

Write your code here

Weekly Project: Unique Word Counter

Let's put everything we've learned about sets into practice by creating a unique word counter.

Your task is to create a program that:

Takes a string of text as input
Splits the text into words
Counts the number of unique words using a set
Prints the total number of words and the number of unique words
Prints the unique words in alphabetical order

Here's a starting template:

def count_unique_words(text):
    # Your code here
    pass

# Test the function
sample_text = "The quick brown fox jumps over the lazy dog. The dog barks, and the fox runs away."
result = count_unique_words(sample_text)
print(result)
            

Implement the count_unique_words function. Here are some hints:

Use the split() method to separate words
Convert words to lowercase to avoid counting "The" and "the" as different words
Use a set to store unique words
Return a tuple containing the total word count, unique word count, and sorted list of unique words

This project will give you hands-on experience with sets and reinforce the concepts we've covered this week. Good luck!

Starter code

# Implement your Unique Word Counter here

Write your code here

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