A set is a collection of unique data. That is, elements of a set cannot be duplicate. For example,

Suppose we want to store information about **student IDs**. Since **student IDs** cannot be duplicate, we can use a set.

## Create a Set in Python

In Python, we create sets by placing all the elements inside curly braces `{}`

, separated by comma.

A set can have any number of items and they may be of different types (integer, float, tuple, string etc.). But a set cannot have mutable elements like lists, sets or dictionaries as its elements.

Let's see an example,

```
# create a set of integer type
student_id = {112, 114, 116, 118, 115}
print('Student ID:', student_id)
# create a set of string type
vowel_letters = {'a', 'e', 'i', 'o', 'u'}
print('Vowel Letters:', vowel_letters)
# create a set of mixed data types
mixed_set = {'Hello', 101, -2, 'Bye'}
print('Set of mixed data types:', mixed_set)
```

**Output**

Student ID: {112, 114, 115, 116, 118} Vowel Letters: {'u', 'a', 'e', 'i', 'o'} Set of mixed data types: {'Hello', 'Bye', 101, -2}

In the above example, we have created different types of sets by placing all the elements inside the curly braces `{}`

.

**Note:** When you run this code, you might get output in a different order. This is because the set has no particular order.

## Create an Empty Set in Python

Creating an empty set is a bit tricky. Empty curly braces `{}`

will make an empty dictionary in Python.

To make a set without any elements, we use the `set()`

function without any argument. For example,

```
# create an empty set
empty_set = set()
# create an empty dictionary
empty_dictionary = { }
# check data type of empty_set
print('Data type of empty_set:', type(empty_set))
# check data type of dictionary_set
print('Data type of empty_dictionary', type(empty_dictionary))
```

**Output**

Data type of empty_set: <class 'set'> Data type of empty_dictionary <class 'dict'>

Here,

`empty_set`- an empty set created using`set()`

`empty_dictionary`- an empty dictionary created using`{}`

Finally we have used the `type()`

function to know which class `empty_set` and `empty_dictionary` belong to.

## Duplicate Items in a Set

Let's see what will happen if we try to include duplicate items in a set.

```
numbers = {2, 4, 6, 6, 2, 8}
print(numbers) # {8, 2, 4, 6}
```

Here, we can see there are no duplicate items in the set as a set cannot contain duplicates.

## Add and Update Set Items in Python

Sets are mutable. However, since they are unordered, indexing has no meaning.

We cannot access or change an element of a set using indexing or slicing. Set data type does not support it.

### Add Items to a Set in Python

In Python, we use the `add()`

method to add an item to a set. For example,

```
numbers = {21, 34, 54, 12}
print('Initial Set:',numbers)
# using add() method
numbers.add(32)
print('Updated Set:', numbers)
```

**Output**

Initial Set: {34, 12, 21, 54} Updated Set: {32, 34, 12, 21, 54}

In the above example, we have created a set named `numbers`. Notice the line,

`numbers.add(32)`

Here, `add()`

adds **32** to our set.

### Update Python Set

The `update()`

method is used to update the set with items other collection types (lists, tuples, sets, etc). For example,

```
companies = {'Lacoste', 'Ralph Lauren'}
tech_companies = ['apple', 'google', 'apple']
companies.update(tech_companies)
print(companies)
# Output: {'google', 'apple', 'Lacoste', 'Ralph Lauren'}
```

Here, all the unique elements of `tech_companies`

are added to the `companies`

set.

## Remove an Element from a Set

We use the `discard()`

method to remove the specified element from a set. For example,

```
languages = {'Swift', 'Java', 'Python'}
print('Initial Set:',languages)
# remove 'Java' from a set
removedValue = languages.discard('Java')
print('Set after remove():', languages)
```

**Output**

Initial Set: {'Python', 'Swift', 'Java'} Set after remove(): {'Python', 'Swift'}

Here, we have used the `discard()`

method to remove `'Java'`

from the `languages` set.

## Built-in Functions with Set

Built-in functions like `all()`

, `any()`

, `enumerate()`

, `len()`

, `max()`

, `min()`

, `sorted()`

, `sum()`

etc. are commonly used with sets to perform different tasks.

Function | Description |
---|---|

all() | Returns `True` if all elements of the set are true (or if the set is empty). |

any() | Returns `True` if any element of the set is true. If the set is empty, returns `False` . |

enumerate() | Returns an enumerate object. It contains the index and value for all the items of the set as a pair. |

len() | Returns the length (the number of items) in the set. |

max() | Returns the largest item in the set. |

min() | Returns the smallest item in the set. |

sorted() | Returns a new sorted list from elements in the set(does not sort the set itself). |

sum() | Returns the sum of all elements in the set. |

## Iterate Over a Set in Python

```
fruits = {"Apple", "Peach", "Mango"}
# for loop to access each fruits
for fruit in fruits:
print(fruit)
```

**Output**

Mango Peach Apple

## Find Number of Set Elements

We can use the `len()`

method to find the number of elements present in a Set. For example,

```
even_numbers = {2,4,6,8}
print('Set:',even_numbers)
# find number of elements
print('Total Elements:', len(even_numbers))
```

**Output**

Set: {8, 2, 4, 6} Total Elements: 4

Here, we have used the `len()`

method to find the number of elements present in a Set.

## Python Set Operations

Python Set provides different built-in methods to perform mathematical set operations like union, intersection, subtraction, and symmetric difference.

### Union of Two Sets

The union of two sets **A** and **B** include all the elements of set **A** and **B**.

We use the `|`

operator or the `union()`

method to perform the set union operation. For example,

```
# first set
A = {1, 3, 5}
# second set
B = {0, 2, 4}
# perform union operation using |
print('Union using |:', A | B)
# perform union operation using union()
print('Union using union():', A.union(B))
```

**Output**

Union using |: {0, 1, 2, 3, 4, 5} Union using union(): {0, 1, 2, 3, 4, 5}

**Note**: `A|B`

and `union()`

is equivalent to `A ⋃ B`

set operation.

### Set Intersection

The intersection of two sets **A** and **B** include the common elements between set **A** and **B**.

In Python, we use the `&`

operator or the `intersection()`

method to perform the set intersection operation. For example,

```
# first set
A = {1, 3, 5}
# second set
B = {1, 2, 3}
# perform intersection operation using &
print('Intersection using &:', A & B)
# perform intersection operation using intersection()
print('Intersection using intersection():', A.intersection(B))
```

**Output**

Intersection using &: {1, 3} Intersection using intersection(): {1, 3}

**Note**: `A&B`

and `intersection()`

is equivalent to `A ⋂ B`

set operation.

### Difference between Two Sets

The difference between two sets **A** and **B** include elements of set **A** that are not present on set **B**.

We use the `-`

operator or the `difference()`

method to perform the difference between two sets. For example,

```
# first set
A = {2, 3, 5}
# second set
B = {1, 2, 6}
# perform difference operation using &
print('Difference using &:', A - B)
# perform difference operation using difference()
print('Difference using difference():', A.difference(B))
```

**Output**

Difference using &: {3, 5} Difference using difference(): {3, 5}

**Note**: `A - B`

and `A.difference(B)`

is equivalent to `A - B`

set operation.

### Set Symmetric Difference

The symmetric difference between two sets **A** and **B** includes all elements of **A** and **B** without the common elements.

In Python, we use the `^`

operator or the `symmetric_difference()`

method to perform symmetric difference between two sets. For example,

```
# first set
A = {2, 3, 5}
# second set
B = {1, 2, 6}
# perform difference operation using &
print('using ^:', A ^ B)
# using symmetric_difference()
print('using symmetric_difference():', A.symmetric_difference(B))
```

**Output**

using ^: {1, 3, 5, 6} using symmetric_difference(): {1, 3, 5, 6}

## Check if two sets are equal

We can use the `==`

operator to check whether two sets are equal or not. For example,

```
# first set
A = {1, 3, 5}
# second set
B = {3, 5, 1}
# perform difference operation using &
if A == B:
print('Set A and Set B are equal')
else:
print('Set A and Set B are not equal')
```

**Output**

Set A and Set B are equal

In the above example, `A` and `B` have the same elements, so the condition

`if A == B`

evaluates to `True`

. Hence, the statement `print('Set A and Set B are equal')`

inside the `if`

is executed.

## Other Python Set Methods

There are many set methods, some of which we have already used above. Here is a list of all the methods that are available with the set objects:

Method | Description |
---|---|

add() | Adds an element to the set |

clear() | Removes all elements from the set |

copy() | Returns a copy of the set |

difference() | Returns the difference of two or more sets as a new set |

difference_update() | Removes all elements of another set from this set |

discard() | Removes an element from the set if it is a member. (Do nothing if the element is not in set) |

intersection() | Returns the intersection of two sets as a new set |

intersection_update() | Updates the set with the intersection of itself and another |

isdisjoint() | Returns `True` if two sets have a null intersection |

issubset() | Returns `True` if another set contains this set |

issuperset() | Returns `True` if this set contains another set |

pop() | Removes and returns an arbitrary set element. Raises `KeyError` if the set is empty |

remove() | Removes an element from the set. If the element is not a member, raises a `KeyError` |

symmetric_difference() | Returns the symmetric difference of two sets as a new set |

symmetric_difference_update() | Updates a set with the symmetric difference of itself and another |

union() | Returns the union of sets in a new set |

update() | Updates the set with the union of itself and others |