- 📘 Day 7
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- Creating a Set
- Getting Set's Length
- Accessing Items in a Set
- Checking an Item
- Adding Items to a Set
- Removing Items from a Set
- Clearing Items in a Set
- Deleting a Set
- Converting List to Set
- Joining Sets
- Finding Intersection Items
- Checking Subset and Super Set
- Checking the Difference Between Two Sets
- Finding Symmetric Difference Between Two Sets
- Joining Sets
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Set is a collection of items. Let me take you back to your elementary or high school Mathematics lesson. The Mathematics definition of a set can be applied also in Python. Set is a collection of unordered and un-indexed distinct elements. In Python set is used to store unique items, and it is possible to find the union, intersection, difference, symmetric difference, subset, super set and disjoint set among sets.
We use curly brackets, {} to create a set or the set() built-in function.
- Creating an empty set
# syntax
st = {}
# or
st = set()- Creating a set with initial items
# syntax
st = {'item1', 'item2', 'item3', 'item4'}Example:
# syntax
fruits = {'banana', 'kiwi', 'mango', 'lemon'}We use len() method to find the length of a set.
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
len(set)Example:
fruits = {'banana', 'kiwi', 'mango', 'lemon'}
len(fruits)We use loops to access items. We will see this in loop section
To check if an item exist in a list we use in membership operator.
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
print("Does set st contain item3? ", 'item3' in st) # Does set st contain item3? TrueExample:
fruits = {'banana', 'kiwi', 'mango', 'lemon'}
print('kiwi' in fruits ) # TrueOnce a set is created we cannot change any items and we can also add additional items.
- Add one item using add()
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
st.add('item5')Example:
fruits = {'banana', 'kiwi', 'mango', 'lemon'}
fruits.add('lime')- Add multiple items using update() The update() allows to add multiple items to a set. The update() takes a list argument.
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
st.update(['item5','item6','item7'])Example:
fruits = {'banana', 'kiwi', 'mango', 'lemon'}
vegetables = ('potato', 'cabbage','onion', 'carrot')
fruits.update(vegetables)We can remove an item from a set using remove() method. If the item is not found remove() method will raise errors, so it is good to check if the item exist in the given set. However, discard() method doesn't raise any errors.
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
st.remove('item2')The pop() methods remove a random item from a list and it returns the removed item.
Example:
fruits = {'banana', 'kiwi', 'mango', 'lemon'}
fruits.pop() # removes a random item from the setIf we are interested in the removed item.
fruits = {'banana', 'kiwi', 'mango', 'lemon'}
removed_item = fruits.pop() If we want to clear or empty the set we use clear method.
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
st.clear()Example:
fruits = {'banana', 'kiwi', 'mango', 'lemon'}
fruits.clear()
print(fruits) # set()If we want to delete the set itself we use del operator.
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
del stExample:
fruits = {'banana', 'kiwi', 'mango', 'lemon'}
del fruitsWe can convert list to set and set to list. Converting list to set removes duplicates and only unique items will be reserved.
# syntax
lst = ['item1', 'item2', 'item3', 'item4', 'item1']
st = set(lst) # {'item2', 'item4', 'item1', 'item3'} - the order is random, because sets in general are unorderedExample:
fruits = ['banana', 'kiwi', 'mango', 'lemon','orange', 'banana']
fruits = set(fruits) # {'mango', 'lemon', 'banana', 'orange'}We can join two sets using the union() or update() method.
- Union This method returns a new set
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item5', 'item6', 'item7', 'item8'}
st3 = st1.union(st2)Example:
fruits = {'banana', 'kiwi', 'mango', 'lemon'}
vegetables = {'potato', 'cabbage','onion', 'carrot'}
print(fruits.union(vegetables)) # {'lemon', 'carrot', 'banana', 'mango', 'kiwi', 'cabbage', 'potato', 'onion'}- Update This method inserts a set into a given set
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item5', 'item6', 'item7', 'item8'}
st1.update(st2) # st2 contents are added to st1Example:
fruits = {'banana', 'kiwi', 'mango', 'lemon'}
vegetables = {'tomato', 'potato', 'cabbage','onion', 'carrot'}
fruits.update(vegetables)
print(fruits) # {'lemon', 'carrot', 'tomato', 'banana', 'mango', 'kiwi', 'cabbage', 'potato', 'onion'}Intersection returns a set of items which are in both the sets. See the example
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item3', 'item2'}
st1.intersection(st2) # {'item3', 'item2'}Example:
whole_numbers = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
even_numbers = {0, 2, 4, 6, 8, 10}
whole_numbers.intersection(even_numbers) # {0, 2, 4, 6, 8, 10}
python = {'p', 'y', 't', 'h', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.intersection(dragon) # {'o', 'n'}A set can be a subset or super set of other sets:
- Subset: issubset()
- Super set: issuperset
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item2', 'item3'}
st2.issubset(st1) # True
st1.issuperset(st2) # TrueExample:
whole_numbers = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
even_numbers = {0, 2, 4, 6, 8, 10}
whole_numbers.issubset(even_numbers) # False, because it is a super set
whole_numbers.issuperset(even_numbers) # True
python = {'p', 'y', 't', 'h', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.issubset(dragon) # FalseIt returns the difference between two sets.
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item2', 'item3'}
st2.difference(st1) # set()
st1.difference(st2) # {'item1', 'item4'} => st1\st2Example:
whole_numbers = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
even_numbers = {0, 2, 4, 6, 8, 10}
whole_numbers.difference(even_numbers) # {1, 3, 5, 7, 9}
python = {'p', 'y', 't', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.difference(dragon) # {'p', 'y', 't'} - the result is unordered (characteristic of sets)
dragon.difference(python) # {'d', 'r', 'a', 'g'}It returns the the symmetric difference between two sets. It means that it returns a set that contains all items from both sets, except items that are present in both sets, mathematically: (A\B) ∪ (B\A)
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item2', 'item3'}
# it means (A\B)∪(B\A)
st2.symmetric_difference(st1) # {'item1', 'item4'}Example:
whole_numbers = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
some_numbers = {1, 2, 3, 4, 5}
whole_numbers.symmetric_difference(some_numbers) # {0, 6, 7, 8, 9, 10}
python = {'p', 'y', 't', 'h', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.symmetric_difference(dragon) # {'r', 't', 'p', 'y', 'g', 'a', 'd', 'h'}If two sets do not have a common item or items we call them disjoint sets. We can check if two sets are joint or disjoint using isdisjoint() method.
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item2', 'item3'}
st2.isdisjoint(st1) # FalseExample:
even_numbers = {0, 2, 4 ,6, 8}
even_numbers = {1, 3, 5, 7, 9}
even_numbers.isdisjoint(odd_numbers) # True, because no common item
python = {'p', 'y', 't', 'h', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.isdisjoint(dragon) # False, there are common items {'o', 'n'}