Data Structures

 Data Structures allow us to store and organize data efficiently.

This will allow us to easily access and perform operations on the data.

In Python, there are four built-in data structures

• List
• Tuple
• Set
• Dictionary

List

List is the most versatile python data structure. Holds an ordered sequence of items.

Creating a List

Created by enclosing elements within [square] brackets. Each item is separated by a comma.

Code

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a = 2

list_a = [5, "Six", a, 8.2]

print(type(list_a))

print(list_a)

PYTHON

Output

<class 'list'>

[5, 'Six', 2, 8.2]

Creating a List of Lists

Code

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a = 2

list_a = [5, "Six", a, 8.2]

list_b = [1, list_a]

print(list_b)

PYTHON

Output

[1, [5, 'Six', 2, 8.2]]

Length of a List

Code

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a = 2

list_a = [5, "Six", a, 8.2]

print(len(list_a))

PYTHON

Output

4

Accessing List Items

To access elements of a list, we use Indexing.

Code

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a = 2

list_a = [5, "Six", a, 8.2]

print(list_a[1])

PYTHON

Output

Six

Iterating Over a List

Code

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a = 2

list_a = [5, "Six", a, 8.2]

for item in list_a:

print(item)

PYTHON

Output

5

Six

2

8.2

List Concatenation

Similar to strings,

+

operator concatenates lists.

Code

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list_a = [1, 2, 3]

list_b = ["a", "b", "c"]

list_c = list_a + list_b

print(list_c)

PYTHON

Output

[1, 2, 3, 'a', 'b', 'c']

Adding Items to List

Code

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5

list_a = []

print(list_a)

for i in range(1,4):

list_a += [i]

print(list_a)

PYTHON

Output

[]

[1, 2, 3]

Repetition

*

Operator repeats lists.

Code

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list_a = [1, 2]

list_b = list_a * 3

print(list_b)

PYTHON

Output

[1, 2, 1, 2, 1, 2]

List Slicing

Obtaining a part of a list is called List Slicing.

Code

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list_a = [5, "Six", 2, 8.2]

list_b = list_a[:2]

print(list_b)

PYTHON

Output

[5, 'Six']

Extended Slicing

Similar to string extended slicing, we can extract alternate items using step.

Code

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list_a = ["R", "B", "G", "O", "W"]

list_b = list_a[0:5:3]

print(list_b)

PYTHON

Output

['R', 'O']

Converting to List

list(sequence)

takes a sequence and converts it into list.

Code

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color = "Red"

list_a = list(color)

print(list_a)

PYTHON

Output

['R', 'e', 'd']

Code

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list_a = list(range(4))

print(list_a)

PYTHON

Output

[0, 1, 2, 3]

Lists are Mutable

• Lists can be modified.
• Items at any position can be updated.

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list_a = [1, 2, 3, 5]

print(list_a)

list_a[3] = 4

print(list_a)

PYTHON

Output

[1, 2, 3, 5]

[1, 2, 3, 4]

Strings are Immutable

Strings are Immutable (Can’t be modified).

Code

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message = "sea you soon"

message[2] = "e"

print(message)

PYTHON

Output

TypeError: 'str' object does not support item assignment