Sets in Python

  • They are unordered
  • You can increase/decrease their length by adding/removing new members
  • They do not allow duplicate members
  • Can only hold immutable objects

Sets are denoted with {...}

Basic usage

basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}
print(basket)  # show that duplicates have been removed
print(len(basket))
# {'apple', 'pear', 'banana', 'orange'}
# 4

Looping through sets

for item in basket:
    print(item)

"""
apple
pear
banana
orange
"""

Check for membership

basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}
print('apple' in basket)
# True

Remove items from set

remove will raise an error if the specified item does not exist, discard will not

basket.remove('apple')
basket.discard('apricot')
print(basket)
# {'pear', 'banana', 'orange'}

basket.clear()
print(basket)
#set

Add items to a set

basket.add('apricot')
print(basket)
# {'apricot', 'pear', 'banana', 'orange'}

Start with empty set

To declare an empty set you cannot just do:

my_set = {}

You have to use a constructor:

my_set = set()

Apply unions and intersections

s1 = {'apple', 'orange', 'banana'}
s2 = {'grapefruit', 'lime', 'banana'}
print('Union:', s1 | s2)
# Union: {'apple', 'orange', 'grapefruit', 'lime', 'banana'}

print('Intersection:', s1 & s2)
# Intersection: {'banana'}


print('Difference:', s1 - s2)
# Difference: {'orange', 'apple'}

print('Symmetric Difference:', s1 ^ s2)
#Symmetric Difference: {'apple', 'orange', 'grapefruit', 'lime'}
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