Sets, Unique Collections

Automatically deduplicate data and test membership in O(1)

A set is an unordered collection with no duplicate values. It's perfect when you want unique items or need to quickly test whether a value exists.

Creating sets and deduplicationpython

# Create a set with curly braces (like a dict, but no key:value)
fruits = {"apple", "banana", "apple", "orange", "banana"}
print(fruits)   # {'orange', 'banana', 'apple'}  (order not guaranteed, no duplicates)

# Create from a list (great for deduplication)
numbers = [1, 2, 2, 3, 3, 3, 4]
unique = set(numbers)
print(unique)   # {1, 2, 3, 4}

Sets are unordered, you cannot index them with [0]. If you need ordering, convert back to a list: sorted(my_set).

Modifying sets, add, remove, discard

Set operationspython

tags = {"python", "beginner", "tutorial"}

tags.add("intermediate")    # add one item
tags.discard("beginner")    # remove if present (no error if missing)
tags.remove("tutorial")     # remove (raises KeyError if missing)

print(tags)   # {'python', 'intermediate'}

# Fast membership test, O(1) vs O(n) for lists
print("python" in tags)   # True

🤔Quick Check

You have a list with 1000 items. Which is faster for checking if a value exists?

Set math, union, intersection, difference

Set operations (math-style)python

python_devs = {"Alice", "Bob", "Charlie"}
js_devs     = {"Bob", "Diana", "Charlie"}

# Union, everyone
all_devs = python_devs | js_devs
print(all_devs)   # {'Alice', 'Bob', 'Charlie', 'Diana'}

# Intersection, know both
both = python_devs & js_devs
print(both)   # {'Bob', 'Charlie'}

# Difference, Python only (not JS)
python_only = python_devs - js_devs
print(python_only)   # {'Alice'}

🤔Quick Check

What does {1, 2, 3} & {2, 3, 4} return?

🌍In the Real World...

Deduplicating alert notifications so on-call engineers aren't paged 50 times for the same issue. Finding unique IP addresses in access logs. Sets are the right tool whenever uniqueness matters.

Practice Exercises

0/3 solved

Exercise 1 of 3easy

⏱ 00:00

Remove Duplicates

Convert the list to a set to remove duplicates, then sort and print the result.
Given: words = ["cat", "dog", "cat", "bird", "dog", "fish"]Expected output: ['bird', 'cat', 'dog', 'fish']

solution.py

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Exercise 2 of 3easy

⏱ 00:00

Common Skills

Find which skills appear in BOTH job listings.
Given:- job1 = {"Python", "SQL", "Docker", "Git"}- job2 = {"Python", "Kubernetes", "Docker", "AWS"}
Expected output (sorted): ['Docker', 'Python']

solution.py

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Exercise 3 of 3medium

⏱ 00:00

Unique Email Domains

Extract the unique email domains from a list of emails.
Given: emails = ["alice@gmail.com", "bob@yahoo.com", "carol@gmail.com", "dave@outlook.com"]Expected output (sorted): ['gmail.com', 'outlook.com', 'yahoo.com']

solution.py

3 / 3

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