#Python's set

A set is a fundamental mathematical model representing a collection of distinct objects. It is similar to a dictionary with only keys — in simple terms, elements in a set are unique.

Set literals are defined using curly braces ({}) with a group of values, for example:

fruits:set[str] = {'Apple', 'Orange', 'Strawberry', 'Banana', 'Pineapple'}

The type annotation set[str] means a set where the element type is str.

#Empty Set

To create an empty set, use set() instead of {}, as the latter creates an empty dictionary.

#Creating Sets from a List or Tuple

You can create a set from a list or tuple. Duplicate values in the source will be filtered out, effectively deduplicating the data:

numbers_list:list[int] = [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5, 8, 9, 7, 9, 3, 2, 3, 8, 4, 6]
numbers_set:set[int] = set(numbers_list)
print(numbers_list)
print(numbers_set)

numbers_list = list(numbers_set)
print(numbers_list)
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#Checking Element Existence

Just like dictionaries, you can use in to check if an element exists in a set:

fruits:set[str] = {'Apple', 'Orange', 'Strawberry', 'Banana', 'Pineapple'}
print('Strawberry' in fruits)
print('Strawberry' not in fruits)
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#Adding Elements

Use the add method to add elements:

fruits:set[str] = {'Apple', 'Orange', 'Strawberry', 'Banana', 'Pineapple'}
fruits.add('Grape')
print(fruits)
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#Removing Elements

Use remove or discard to delete elements:

• remove – deletes the specified element, raises an error if not found.
• discard – deletes the specified element, does nothing if not found.

fruits:set[str] = {'Apple', 'Orange', 'Strawberry', 'Banana', 'Pineapple'}
fruits.remove('Apple')          # Remove 'Apple'
fruits.discard('Banana')        # Remove 'Banana'
print(fruits)
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#Clearing a Set

Use the clear method to remove all elements:

fruits:set[str] = {'Apple', 'Orange', 'Strawberry', 'Banana', 'Pineapple'}
fruits.clear()
print(fruits)
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#Merging Sets

Use the update method to merge another set:

fruits:set[str] = {'Apple', 'Orange', 'Strawberry'}
fruits.update({'Banana', 'Pineapple'})
print(fruits)
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#Intersection

Use the intersection method or & operator to get the intersection of sets (elements common to both):

• Both methods return a new set without modifying the original.
• Use intersection_update to modify the original set in place.

fruits:set[str] = {'Apple', 'Orange', 'Strawberry', 'Tomato', 'Cucumber'}
vegetables:set[str] = {'Cabbage', 'Tomato', 'Cucumber', 'Spinach'}

print(fruits.intersection(vegetables))
print(fruits & vegetables)
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#Union

Use the union method or | operator to get the union of sets (all unique elements from both):

• Both methods return a new set without modifying the original.
• Use update to modify the original set in place.

fruits:set[str] = {'Apple', 'Orange', 'Strawberry', 'Tomato', 'Cucumber'}
vegetables:set[str] = {'Cabbage', 'Tomato', 'Cucumber', 'Spinach'}

print(fruits.union(vegetables))
print(fruits | vegetables)
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#Difference

Use the difference method or - operator to get the difference (elements only in the first set):

• Both methods return a new set without modifying the original.
• Use difference_update to modify the original set in place.

fruits:set[str] = {'Apple', 'Orange', 'Strawberry', 'Tomato', 'Cucumber'}
vegetables:set[str] = {'Cabbage', 'Tomato', 'Cucumber', 'Spinach'}

print(fruits.difference(vegetables))
print(fruits - vegetables)
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#Symmetric Difference

Use the symmetric_difference method to get the symmetric difference (elements unique to each set):

• Both methods return a new set without modifying the original.
• Use symmetric_difference_update to modify the original set in place.

fruits:set[str] = {'Apple', 'Orange', 'Strawberry', 'Tomato', 'Cucumber'}
vegetables:set[str] = {'Cabbage', 'Tomato', 'Cucumber', 'Spinach'}

print(fruits.symmetric_difference(vegetables))
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#Subsets and Supersets

If all elements of set A are in set B, then A is a subset of B, and B is a superset of A. If A and B are not equal, then A is a proper subset of B, and B is a proper superset of A.

Python uses comparison operators to check set relationships: