Python Sets

A set in Python is a collection data type.

Key Features of Sets

1. Unordered: The items in a set have no defined order.
2. Unindexed: You cannot access items in a set by index.
3. Unique: No duplicate elements are allowed.
4. Mutable: You can add and remove items.

How to Define a Set

Sets are implemented using a hash table, making membership testing and operations like union and intersection very fast.

1. Creating a Set Using Curly Braces {}:

   Copymy_set = {1, 2, 3, 4}
   print(my_set)  # Output: {1, 2, 3, 4}
   

2. Using set() Constructor:

   Copymy_set = set([1, 2, 2, 3])  # Duplicates are removed
       print(my_set)  # Output: {1, 2, 3}
   
       empty_set = set()  # Creates an empty set
   

Basic Operations on Sets

1. Adding Elements
• add(element): Adds a single element to the set.

  Copymy_set = {1, 2, 3}
      my_set.add(4)
      print(my_set)  # Output: {1, 2, 3, 4}
  

2. Removing Elements
• remove(element): Removes the specified element. Raises KeyError if the element is not found.

  Copymy_set.remove(2)
  
  discard(element): Removes the specified element without raising an error if it does not exist.
  
  my_set.discard(5)  # No error even if 5 is not in the set
  

• pop(): Removes and returns an arbitrary element from the set.

  Copyremoved_item = my_set.pop()
  print(removed_item)
  

• clear(): Removes all elements from the set.

  Copymy_set.clear()
  

Set Advance Operations

1. Union Combines all unique elements from both sets:

   Copyset1 = {1, 2, 3}
   set2 = {3, 4, 5}
   print(set1 | set2)             # Output: {1, 2, 3, 4, 5}
   print(set1.union(set2))        # Output: {1, 2, 3, 4, 5}
   

2. Intersection Returns elements common to both sets:

   Copyprint(set1 & set2)             # Output: {3}
   print(set1.intersection(set2)) # Output: {3}
   

3. Difference Returns elements in the first set but not in the second:

   Copyprint(set1 - set2)             # Output: {1, 2}
   print(set1.difference(set2))   # Output: {1, 2}
   

4. Symmetric Difference Returns elements in either set but not in both:

   Copyprint(set1 ^ set2)                      # Output: {1, 2, 4, 5}
   print(set1.symmetric_difference(set2))  # Output: {1, 2, 4, 5}
   

Membership Testing

Copymy_set = {1, 2, 3}
print(1 in my_set)    # Output: True
print(5 not in my_set)  # Output: True

Iterating Through a Set

Copymy_set = {1, 2, 3}
for item in my_set:
    print(item)

Frozenset

A frozenset is an immutable version of a set. Once created, its elements cannot be modified.

Copyfs = frozenset([1, 2, 3])
print(fs)  # Output: frozenset({1, 2, 3})
# fs.add(4)  # Raises an AttributeError

Set Methods

Examples of Usage

1. Removing Duplicates from a List

   Copynumbers = [1, 2, 2, 3, 4, 4]
   unique_numbers = set(numbers)
   print(unique_numbers)  # Output: {1, 2, 3, 4}
   

2. Finding Common Items Between Two Lists

   Copylist1 = [1, 2, 3]
   list2 = [3, 4, 5]
   common_items = set(list1) & set(list2)
   print(common_items)  # Output: {3}
   

When to Use Sets

1. Removing duplicates from a collection.
2. Performing fast membership testing.
3. Working with mathematical set operations.
4. Use cases where element ordering or duplicates are not required.

Sets are highly efficient for tasks requiring uniqueness and membership tests!