Sets

Sets in Python are unordered collections of unique elements. They are similar to lists or dictionaries, but with key differences, such as disallowing duplicate elements and not maintaining any order. Sets are particularly useful when you need to eliminate duplicates, perform membership tests, or apply mathematical set operations like union, intersection, and difference.

Creating Sets

You can create a set by using curly braces {} or the set() function.

• Using Curly Braces:

  my_set = {1, 2, 3, 4}
  # my_set is {1, 2, 3, 4}
  

• Using the set() Function:

  my_set = set([1, 2, 3, 4])
  # my_set is {1, 2, 3, 4}
  

• Creating an Empty Set:

  • Use set() to create an empty set (curly braces {} would create an empty dictionary instead).

  empty_set = set()
  # empty_set is set()
  

Key Characteristics

1. Unique Elements:

   • Sets automatically eliminate duplicate values.

   my_set = {1, 2, 2, 3}
   # my_set is {1, 2, 3}
   

2. Unordered:

   • The elements in a set are not stored in any particular order, and their order can change.

   my_set = {3, 1, 2}
   # my_set could be displayed as {1, 2, 3} or any other order
   

3. Immutable Elements:

   • Sets can only contain immutable (hashable) elements like numbers, strings, and tuples, but not lists or other sets.

   my_set = {1, "Hello", (2, 3)}
   # This is valid
   # my_set = {[1, 2], 3} would raise a TypeError
   

Common Set Operations

1. Adding Elements:

   • Use add() to add a single element to a set.

   my_set = {1, 2}
   my_set.add(3)
   # my_set is {1, 2, 3}
   

2. Removing Elements:

   • Use remove() to remove a specific element. Raises KeyError if the element is not found.
   • Use discard() to remove an element without raising an error if it’s not found.

   my_set = {1, 2, 3}
   my_set.remove(2)
   # my_set is {1, 3}
   
   my_set.discard(4)  # No error raised
   

3. Set Union:

   • Combine two sets using the | operator or union() method.

   set1 = {1, 2, 3}
   set2 = {3, 4, 5}
   union_set = set1 | set2
   # union_set is {1, 2, 3, 4, 5}
   

4. Set Intersection:

   • Find common elements between two sets using the & operator or intersection() method.

   set1 = {1, 2, 3}
   set2 = {2, 3, 4}
   intersection_set = set1 & set2
   # intersection_set is {2, 3}
   

5. Set Difference:

   • Find elements in one set but not in the other using the - operator or difference() method.

   set1 = {1, 2, 3}
   set2 = {2, 3, 4}
   difference_set = set1 - set2
   # difference_set is {1}
   

6. Set Symmetric Difference:

   • Find elements that are in either of the sets but not in both using the ^ operator or symmetric_difference() method.

   set1 = {1, 2, 3}
   set2 = {3, 4, 5}
   symmetric_difference_set = set1 ^ set2
   # symmetric_difference_set is {1, 2, 4, 5}
   

Membership Tests

Sets are highly efficient for membership tests, meaning you can quickly check if an element is in a set.

• Checking Membership:

  my_set = {1, 2, 3}
  is_member = 2 in my_set  # True
  not_member = 4 not in my_set  # True
  

Set Comprehensions

Similar to list comprehensions, you can use set comprehensions to create sets in a concise manner.

• Example:

  squared_set = {x**2 for x in range(5)}
  # squared_set is {0, 1, 4, 9, 16}