What are sets? Sets are collections that only store unique values. They automatically remove duplicates.
Think of sets like:
A bag of unique marbles
Guest list (each person once)
Unique tags or categories
Creating sets You can create sets two ways: with set() or with curly braces {} (but only when it has values).
# Empty set (careful!) empty_set = set () # NOT {} - that's a dict! # Set with values - both ways work numbers = { 1 , 2 , 3 , 4 , 5 } fruits = set ([ "apple" , "banana" , "orange" ]) # From a list (removes duplicates) scores = [ 85 , 90 , 85 , 92 , 90 ] unique_scores = set (scores) # {85, 90, 92} Use set() for empty sets, not {}. Empty curly braces create a dictionary!
Basic operations colors = { "red" , "blue" } # Add items colors.add( "green" ) print (colors) # {'red', 'blue', 'green'} # Remove items colors.remove( "blue" ) # Error if not found colors.discard( "yellow" ) # No error if not found # Check membership if "red" in colors: print ( "Red is available" ) Common uses Remove duplicates names = [ "Alice" , "Bob" , "Alice" , "Charlie" , "Bob" ] unique_names = list ( set (names)) print (unique_names) # ['Alice', 'Bob', 'Charlie'] Fast membership testing allowed_users = { "alice" , "bob" , "charlie" } if "alice" in allowed_users: # Very fast! print ( "Access granted" ) Common mistakes
# Wrong - creates empty dict empty = {} # Right - use set() empty = set ()
# Order is not guaranteed! numbers = { 3 , 1 , 4 , 1 , 5 } print (numbers) # Could be any order # Use list if order matters ordered = [ 3 , 1 , 4 , 1 , 5 ] What’s next? Congratulations! You’ve completed Python Basics. Ready to start building programs?
Building Programs Learn about functions
