Create set

First, we create a collection by listing its elements in curly braces. The only exception is the empty set() that can be formed with the help of the function:

empty_set = set()
print(type(empty_set))   # <class 'set'>

empty_dict = {}
print(type(empty_dict))  # <class 'dict'>

If you pass a string or list to set(), the function returns a collection containing all the elements of the string / list:

flowers = {'rose', 'lilac', 'daisy'}

# the order is not preserved
print(flowers)  # {'daisy', 'lilac', 'rose'}  


letters = set('philharmonic')
print(letters)  # {'h', 'r', 'i', 'c', 'o', 'l', 'a', 'p', 'm', 'n'}

Each element is considered only part of a set, so double letters are counted as one element:

letters = set('Hello')
print(len(letters))  # the length equals 4
print(letters)       # {'H', 'e', 'o', 'l'}

In addition, using collections can help you avoid duplication:

states = ['Russia', 'USA', 'USA', 'Germany', 'Italy']
print(set(states))  # {'Russia', 'USA', 'Italy', 'Germany'}

Take a look: since the order of named elements has no effect, the following two groups will be equal.

set1 = {'A', 'B', 'C'}
set2 = {'B', 'C', 'A'}
print(set1 == set2)  # True

Use the elements of the collection

• Get the number of collection elements with the help of len() function.
• Use the for loop to iterate through all elements.
• Check whether the element belongs to a specific set (in / not in operator), and you will get a Boolean value.

nums = {1, 2, 2, 3}
print(1 in nums, 4 not in nums)  # True True

• add() uses the method or update() uses another collection to add a new element to the collection

nums = {1, 2, 2, 3}
nums.add(5)
print(nums)  # {1, 2, 3, 5}

another_nums = {6, 7}
nums.update(another_nums)
print(nums)  # {1, 2, 3, 5, 6, 7}
 
# we can also add a list
text = ['how', 'are', 'you']
nums.update(text)
print(nums)  # {'you', 1, 2, 3, 5, 6, 7, 'are', 'how'}
 
# or a string
word = 'hello'
nums.add(word)
print(nums)  # {1, 2, 3, 'how', 5, 6, 7, 'hello', 'you', 'are'}

Note that when we update a collection with a list, these are the list elements added to the collection, not the list itself.

• The discard/remove method is used to remove elements from a specific collection. The only difference between their operations is that there is no element to delete in the collection. In this case, discard does not perform any operation and remove generates a KeyError exception.

nums.remove(2)
print(nums)  # {1, 3, 5}

empty_set = set()
empty_set.discard(2)  # nothing happened
empty_set.remove(2)   # KeyError: 2

• Use the method to delete a random element pop(). Since it will be random, you do not need to select parameters.

nums = {1, 2, 2, 3}
nums.pop()
print(nums)  # {2, 3}

• clear() uses the method to delete all elements from the collection.