Python Sets and Set Methods

2. 🔎 Accessing and Checking Set Items

2.1 Sets Do Not Support Indexing
1. Sets are unordered, so items do not have fixed positions. Because of this, indexing is not allowed. Example: my_set = {"apple", "banana", "orange"} print(my_set[0]) # ➜ TypeError ⚠️ This line gives an error because set items cannot be accessed using index. 📌 Use a list or tuple when position matters. 📌 Use a set when uniqueness matters.
2.2 Checking Membership using in
1. We can check whether an item exists in a set using in. Example: my_set = {"apple", "banana", "orange"}print("apple" in my_set) # ➜ True print("mango" in my_set) # ➜ False
2.3 Checking Non-Membership using not in
1. We can check whether an item does not exist in a set using not in. Example: my_set = {"apple", "banana", "orange"}print("mango" not in my_set) # ➜ True print("banana" not in my_set) # ➜ False

3. ➕➖ Adding and Removing Set Items

3.1 add()
1. add() is used to add one item to a set. It modifies the original set. Example: my_set = {1, 2, 3}my_set.add(4) print(my_set) # ➜ {1, 2, 3, 4} my_set.add(2) print(my_set) # ➜ {1, 2, 3, 4} 📌 Adding a duplicate value does not change the set.
3.2 update()
1. update() is used to add multiple items from another collection such as a list, tuple, or set. It modifies the original set. Example: my_set = {1, 2, 3}my_set.update([4, 5]) print(my_set) # ➜ {1, 2, 3, 4, 5} my_set.update((6, 7)) print(my_set) # ➜ {1, 2, 3, 4, 5, 6, 7} my_set.update({8, 9}) print(my_set) # ➜ {1, 2, 3, 4, 5, 6, 7, 8, 9} 📌 add() adds one item. 📌 update() adds multiple items.

3.3 update() with String
1. A string is also an iterable. So if we use update() with a string, each character is added separately. Example: my_set = {1, 2, 3}my_set.update("hi") print(my_set) # ➜ {1, 2, 3, "h", "i"} 📌 The output order may be different because sets are unordered.
3.4 remove()
1. remove() removes a specified item from a set. It gives an error if the item is not found. Example: my_set = {1, 2, 3, 4}my_set.remove(2) print(my_set) # ➜ {1, 3, 4} my_set.remove(5) # ➜ KeyError ⚠️ This line gives an error because 5 is not found in the set. 📌 KeyError means Python could not find the requested value in the set.
3.5 discard()
1. discard() also removes a specified item from a set. But it does not give an error if the item is not found. Example: my_set = {1, 2, 3, 4}my_set.discard(3) print(my_set) # ➜ {1, 2, 4} my_set.discard(5) print(my_set) # ➜ {1, 2, 4} 📌 remove() gives an error if the item is not found. 📌 discard() does not give an error if the item is not found.

3.6 pop()
1. pop() removes and returns one item from a set. Since sets are unordered, we cannot know which item will be removed. Example: my_set = {1, 2, 3, 4}removed_item = my_set.pop() print(removed_item) # ➜ Could be any item from the set print(my_set) # ➜ Set with one less item 📌 In lists, pop() usually removes the last item. 📌 In sets, pop() removes an arbitrary item because sets are unordered.

4. 🧮 Common Set Functions

4.1 Numeric and Common Functions
1. Some functions are useful for numeric sets, while others work with any set. Common Functions: sum() ➜ Adds all numeric items min() ➜ Finds smallest value max() ➜ Finds largest value len() ➜ Returns the number of items in the set. sorted() ➜ Returns a sorted list copy() ➜ Creates a copy of a set 📌 sum() works only with numeric sets. 📌 min() and max() work when the set items can be compared with each other.
4.2 Numeric Function Examples
1. num_set = {1, 2, 3, 4, 5}print(sum(num_set)) # ➜ 15 print(min(num_set)) # ➜ 1 print(max(num_set)) # ➜ 5 print(len(num_set)) # ➜ 5
4.3 sorted()
1. Sets do not have a fixed order. If we want sorted output, we can use sorted(). sorted() returns a list, not a set. Example: my_set = {3, 1, 4, 2}sorted_data = sorted(my_set) print(sorted_data) # ➜ [1, 2, 3, 4] print(type(sorted_data)) # ➜ <class 'list'> 📌 sorted() does not change the original set. 📌 sorted() returns a list.
4.4 Sorting Strings
1. Example: str_set = {"apple", "ball", "cat"}sorted_str_set = sorted(str_set, reverse=True) print(sorted_str_set) # ➜ ["cat", "ball", "apple"] sorted_by_length = sorted(str_set, key=len) print(sorted_by_length) # ➜ ["cat", "ball", "apple"] 📌 "cat" has 3 letters, "ball" has 4 letters, and "apple" has 5 letters.
4.5 Copying Sets
1. copy() creates a copy of a set. This is useful when we want to modify the copied set without changing the original set. Example: original_set = {1, 2, 3}copied_set = original_set.copy()copied_set.add(4)print(original_set) # ➜ {1, 2, 3} print(copied_set) # ➜ {1, 2, 3, 4}

4.6 Assignment is Not Copy
1. If we assign one set to another variable using =, both variables refer to the same set. Example: original_set = {1, 2, 3}same_set = original_setsame_set.add(4)print(original_set) # ➜ {1, 2, 3, 4} print(same_set) # ➜ {1, 2, 3, 4} 📌 Use copy() when you want a separate set.

5. 🔗 Set Operations

5.1 What are Set Operations?
1. Set operations are used to compare and combine groups of data. Common Set Operations: union() ➜ Combines all unique items intersection() ➜ Finds common items difference() ➜ Finds items present in one set but not another symmetric_difference() ➜ Finds items that are in either set, but not both

5.2 union()
1. union() combines all unique items from two sets. Symbol: |Example: set_a = {1, 2, 3} set_b = {3, 4, 5}print(set_a.union(set_b)) # ➜ {1, 2, 3, 4, 5} print(set_a | set_b) # ➜ {1, 2, 3, 4, 5}
5.3 intersection()
1. intersection() finds common items between two sets. Symbol: &Example: set_a = {1, 2, 3} set_b = {3, 4, 5}print(set_a.intersection(set_b)) # ➜ {3} print(set_a & set_b) # ➜ {3}
5.4 difference()
1. difference() finds items that are in the first set but not in the second set. Symbol: -Example: set_a = {1, 2, 3} set_b = {3, 4, 5}print(set_a.difference(set_b)) # ➜ {1, 2} print(set_a - set_b) # ➜ {1, 2} 📌 set_a - set_b is different from set_b - set_a.
5.5 symmetric_difference()
1. symmetric_difference() finds items that are in either set, but not in both. Symbol: ^Example: set_a = {1, 2, 3} set_b = {3, 4, 5}print(set_a.symmetric_difference(set_b)) # ➜ {1, 2, 4, 5} print(set_a ^ set_b) # ➜ {1, 2, 4, 5}

6. 🧊 Frozenset

6.1 What is frozenset?
1. frozenset is an immutable version of a set. Once created, items cannot be added or removed. Example: my_frozenset = frozenset([1, 2, 3]) print(my_frozenset) # ➜ frozenset({1, 2, 3})
6.2 frozenset is Immutable
1. Example: my_frozenset = frozenset([1, 2, 3]) my_frozenset.add(4) # ➜ AttributeError ⚠️ This line gives an error because frozenset does not have add(). 📌 AttributeError means Python does not allow that action on this data type because the tool or method is not available.