Set

Python has a built-in method called

`set`

. set type has the following characteristics- Sets are a collection which is unordered and unindexed
- Set elements are unique. Duplicate elements are not allowed.
- A set itself may be mutable, but the elements within a set is immutable.

You can create sets in two ways:

- 1.using
`set`

method followed by a parenthesis`()`

. - 2.using
**curly brackets**`{}`

.

`set()`

You can have an **ITERABLE** object such as list or tuple within **set** using

`set(<iter>)`

. This returns the list or tuple as a `set`

wrapped in a curly bracket `{}`

. Any iterable object can be converted to a `set()`

. You can think of `set()`

as `extend()`

method of lists. A list within

`set()`

.Code

Output

numbers = set([1, 2, 3, 4, 5, 6, 7])

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print(numbers)

{1, 2, 3, 4, 5, 6, 7}

A tuple within

`set()`

.Code

Output

numbers = set((1, 2, 3, 4, 5, 6, 7))

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print(numbers)

{1, 2, 3, 4, 5, 6, 7}

A string with

`a set()`

.Code

Output

my_letters = set('ABCDEF')

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print(my_letters)

{'E', 'F', 'C', 'B', 'A', 'D'}

While converting an iterable objects to a set, the returned set is **deduplicated**.

Code

Outputs

# Example 1

my_cities = set(['Krakow', 'Warsaw', 'Warsaw', 'Kielce'])

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print(my_cities)

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# Example 2

my_letters = set('AaBBCCDDEEE')

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print(my_letters)

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# Example 3

my_numbers = set('12345342')

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print(my_numbers)

# Example 1 output

{'Krakow', 'Kielce', 'Warsaw'}

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# Example 2 output

{'D', 'E', 'B', 'C', 'a', 'A'}

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# Example 3 output

{'4', '1', '3', '2', '5'}

You can see that the output are unordered and deduplicated. The original orders are not kept. **iterable** such as a string, list or tuple. For example, integers are not iterable and it raises an error, to be specific

`set()`

only accepts an object that is `TypeError`

, while we try to create a set with integer.Code

Output

my_numbers = set(12345342)

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print(my_numbers)

TypeError Traceback (most recent call last)

<ipython-input-5-2b17322ba0b5> in <module>()

----> 1 my_numbers = set(12345342)

2

3 print(my_numbers)

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TypeError: 'int' object is not iterable

`curly bracket {}`

Code

Outputs

# Example 1

my_cities = {'Krakow', 'Warsaw', 'Warsaw', 'Kielce'}

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print(my_cities)

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# Example 2

my_letters = {'AaBBCCDDEEE'}

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print(my_letters)

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# Example 3

my_numbers = {12345342}

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print(my_numbers)

# Example 1 output

{'Kielce', 'Warsaw', 'Krakow'}

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# Example 2 output

{'AaBBCCDDEEE'}

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# Example 3 output

{12345342}

As you can see, the **curly brackets** do not iterate through iterable elements. Each object is present in the set intact regardless of iterability.

Empty set

set can also be empty, as we had empty list and empty tuple. You can create an empty set using built-in function of set() only because Python interprets empty **curly brackets **

`{}`

as an empty dictionary. Code

Output

empty_set = set()

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# Check empty_set type

print(type(empty_set))

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print(empty_set)

# print(type(empty_set))

<class 'set'>

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# print(empty_set)

set()

Mixed datatypes set

A set can have a mixed datatypes

Code

Output

# set function

mixed_set = set([34, 3.2, 'cat', 1.858, False, True, 'Name'])

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print(mixed_set)

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# Curly brackets

mixed_set_curly = {34, 3.2, 'cat', 1.858, False, True, 'Name'}

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print(mixed_set_curly)

# set function

{False, 1.858, 34, 3.2, True, 'cat', 'Name'}

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# Curly brackets

{False, 1.858, 34, 3.2, True, 'cat', 'Name'}

How to add element(s) to a set?

Sets are unordered and changing with indexing brackets is not possible. Sets are mutable, but we cannot perform slicing or indexing operations to access its elements. Python raises

`TypeError`

when you use indexing or slicing operation.Code

Output

number_set = {1, 2, 3, 4}

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print(number_set[:2])

TypeError Traceback (most recent call last)

<ipython-input-11-c24bd2d35a09> in <module>()

1 number_set = {1, 2, 3, 4}

2

----> 3 print(number_set[:2])

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TypeError: 'set' object is not subscriptable

You can use set method of

`add()`

to add an element. `add()`

method can be used to add an element, it takes only an arguments (`add(<obj>)`

).Code

Output

new_set = {9, 8, 7, 6}

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new_set.add(5)

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print(new_set)

# print(new_set)

{5, 6, 7, 8, 9}

You can use set method

`update()`

to add elements . `update()`

requires an iterable datatype (simple or complex) (`update(<iter>)`

).Code

Output

new_set = {9, 8, 7, 6}

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new_set.update([5, 2, 4, 3])

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print(new_set)

# print(new_set)

{2, 3, 4, 5, 6, 7, 8, 9}

How to delete element(s) from a set?

You can delete an element from a set using

`discard()`

or `remove()`

. remove function

`remove()`

will delete the element where it is present and raises a `KeyError`

where the element is absent. Code

Output

# Element is present

new_set = {9, 8, 7, 6}

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new_set.remove(8)

print(new_set)

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# Element is absent

new_set = {9, 8, 7, 6}

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new_set.remove(5)

print(new_set)

# Element is present

# print(new_set)

{9, 6, 7}

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# Element is absent

# print(new_set)

KeyError Traceback (most recent call last)

<ipython-input-23-25ec930c2723> in <module>()

1 new_set = {9, 8, 7, 6}

2

----> 3 new_set.remove(5)

4

5 print(new_set)

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KeyError: 5

discard function

You can also use

`discard()`

to delete an element. if element is a member of the set, then removes it, but it does nothing when element is not a member of a set.Code

Output

# Element is present

new_set = {9, 8, 7, 6}

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new_set.discard(8)

print(new_set)

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# Element is absent

new_set = {9, 8, 7, 6}

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new_set.discard(5)

print(new_set)

# Element is present

# print(new_set)

{9, 6, 7}

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# Element is absent

# print(new_set)

{8, 9, 6, 7}

pop function

You can use pop() on a set. pop() returns an arbitrary element because sets are unordered.

Code

Ouput

new_set = {9, 8, 5, 4, 7, 6}

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print(new_set.pop())

print(new_set)

print(new_set.pop())

4

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print(new_set)

{5, 6, 7, 8, 9}

Set methods and operators

You can use Python set methods and operators to perform operations such as union, intersection, difference and symmetric difference.

union

The set made by combining the elements of two sets.

Union of set 1 and set 2 is the whole circles.

You can use **.**

**union()**

method or `| operator`

Code

Output

set_1 = {4, 5, 6, 7, 8, 9}

set_2 = {1, 4, 3, 5, 6}

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# method 1

new_set = set_1.union(set_2)

print(new_set)

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# method 2

new_set_2 = set_1 | set_2

print(new_set_2)

# print(new_set)

{1, 3, 4, 5, 6, 7, 8, 9}

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# print(new_set_2)

{1, 3, 4, 5, 6, 7, 8, 9}

`| operator`

creates a union of two sets (both side have to be sets), otherwise, it raises an error. While `union()`

takes an iterable and converts it to a set before performing union operation. See example below; notice that the second set is a tuple. Code

Output

set_1 = {4, 5, 6, 7, 8, 9}

set_2 = (1, 4, 3, 5, 6)

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# method 1

new_set = set_1.union(set_2)

print(new_set)

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# method 2

print(set_1 | set_2)

# print(new_set)

{1, 3, 4, 5, 6, 7, 8, 9}

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#print(set_1 | set_2)

---------------------------------------------------------------------------

TypeError Traceback (most recent call last)

<ipython-input-8-5ce450bc75fa> in <module>()

8

9 # method 2

---> 10 print(set_1 | set_2)

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TypeError: unsupported operand type(s) for |: 'set' and 'tuple'

As you can see, the

`union`

runs successfully but `| operator`

raises `TypeError`

.intersection

set intersection is the elements that are only in both sets or the elements which are **overlapping**.

Intersect of set1 and set 2 (set 1 ^ set 2 section only)

You can use ** **** **to get intersect of two sets.

**intersection()**

method or`& operator`

Code

Output

set_1 = {4, 5, 6, 7, 8, 9}

set_2 = {1, 4, 3, 5, 6}

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# method 1

new_set = set_1.intersection(set_2)

print(new_set)

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# method 2

new_set_2 = set_1 & set_2

print(new_set_2)

# print(new_set)

{4, 5, 6}

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# print(new_set_2)

{4, 5, 6}

You can use ** **** **to get intersect of two sets. The difference of set A and set B is a set of elements that are only present in set A but not set B. The difference of set B and set A is vice versa.

**difference()**

method or`- operator`

set 1 difference

Code

Output

set_1 = {4, 5, 6, 7, 8, 9}

set_2 = {1, 4, 3, 5, 6}

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# method 1

set_1_diff = set_1.difference(set_2)

print(set_1_diff)

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# method 2

set_1_diff_op = set_1 - set_2

print(set_1_diff_op)

# print(set_1_diff)

{7, 8, 9}

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#print(set_1_diff_ops)

{7, 8, 9}

set 2 difference

Code

Output

set_1 = {4, 5, 6, 7, 8, 9}

set_2 = {1, 4, 3, 5, 6}

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# method 1

set_2_diff = set_2.difference(set_1)

print(set_2_diff)

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# method 2

set_2_diff_op = set_2 - set_1

print(set_2_diff_op)

# print(set_2_diff)

{1, 3}

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#print(set_2_diff_ops)

{1, 3}

symmetric difference

symmetric difference is a set that contains all the elements from set A and set B that is not shared. It can be seen as opposite of intersection.

You can You can use

`symmetric_difference()`

method or `^ operator`

.Code

Output

set_1 = {4, 5, 6, 7, 8, 9}

set_2 = {1, 4, 3, 5, 6}

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# method 1

sym_diff = set_1.symmetric_difference(set_2)

print(sym_diff)

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# method 2

sym_diff_op = set_1 ^ set_2

print(sym_diff_op)

# print(sym_diff)

{1, 3, 7, 8, 9}

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#print(sym_diff_ops)

{1, 3, 7, 8, 9}

All set methods and operators above support multiple set union, intersection, difference and symmetric difference when you are using methods and operators except symmetric difference method.

Code

Output

set_1 = {4, 5, 6, 7, 8, 9}

set_2 = {1, 4, 3, 5, 6}

set_3 = {1, 5, 6, 10}

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# method 1

sym_diff_op = set_1 ^ set_2 ^ set_3

print(sym_diff_op)

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# method 2

sym_diff = set_1.symmetric_difference(set_2, set_3)

print(sym_diff)

# print(sym_diff_op)

{3, 5, 6, 7, 8, 9, 10}

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# print(sym_diff)

TypeError Traceback (most recent call last)

<ipython-input-20-cc52d7471fff> in <module>()

9

10 # method 2

---> 11 sym_diff = set_1.symmetric_difference(set_2, set_3)

12 print(sym_diff)

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TypeError: symmetric_difference() takes exactly one argument (2 given)

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Last modified 2yr ago