List is a built-in data structure used to store an ordered collection of items. They are dynamic, resizable and capable of storing multiple data types.

• List elements can be changed, updated, added, or removed after the list is created.
• Elements maintain the order in which they are inserted.
• Elements are accessed using their position, starting from index 0.

Creating a List

Lists can be created in several ways, such as using square brackets [], the list() constructor or by repeating elements.

1. Using Square Brackets: Square brackets [] are used to create a list directly.

a = [1, 2, 3]
print(a)

b = ["apple", "banana"]
print(b)

[1, 2, 3]
['apple', 'banana']

2. Using list() Constructor: A list can also be created by passing an iterable (such as tuple, string or another list) to the list() constructor.

a = list((1, 2, 3, 'apple', 4.5))  
print(a)

b = list("GFG")
print(b)

[1, 2, 3, 'apple', 4.5]
['G', 'F', 'G']

3. Creating List with Repeated Elements: A list with repeated elements can be created using the multiplication (*) operator.

a = [2] * 5
b = [0] * 7

print(a)
print(b)

[2, 2, 2, 2, 2]
[0, 0, 0, 0, 0, 0, 0]

Internal Representation of Lists

Python list stores references to objects, not the actual values directly.

• The list keeps memory addresses of objects like integers, strings or booleans.
• Actual objects exist separately in memory.
• Modifying a mutable object inside a list changes the original object.
• Reassigning an immutable object creates a new object instead of changing the old one.

a = [1, 2, 2, "Python"]
print(a[0])   # index-based
print(a)

1
[1, 2, 2, 'Python']

Explanation:

• a[0] accesses the first element of the list.
• list contains integers and a string, showing that Python lists can store multiple data types.

Accessing Elements

Elements in a list are accessed using indexing. Python uses zero-based indexing, meaning a[0] represents the first element. Negative indexing is also supported, where -1 accesses the last element.

a = [10, 20, 30]
print(a[0])
print(a[-1])

10
30

Adding Elements

Elements can be added to a list using the following methods:

1. append(): Adds an element at the end of the list.

a = [1, 2]
a.append(3)
print(a)

[1, 2, 3]

2. insert(): Adds an element at a specific position.

a = [1, 3]
a.insert(1, 2)
print(a)

[1, 2, 3]

3. extend(): Adds multiple elements to the end of the list.

a = [1, 2]
a.extend([3, 4])
print(a)

[1, 2, 3, 4]

Updating Elements

Since lists are mutable, elements can be updated by assigning new values using their index.

a = [10, 20, 30, 40, 50]
a[1] = 25 
print(a)  

[10, 25, 30, 40, 50]

Removing Elements

Elements can be removed from a list using the following methods:

1. remove(): Removes the first occurrence of an element.

a = [1, 2, 3]
a.remove(2)
print(a)

[1, 3]

2. pop(): Removes the element at a specific index or the last element if no index is specified.

a = [1, 2, 3]
a.pop()
print(a)

[1, 2]

3. del statement: Deletes an element at a specified index.

a = [1, 2, 3]
del a[1]
print(a)

[1, 3]

4. clear(): removes all items.

a = [1, 2, 3]
a.clear()
print(a)

[]

Iterating Over Lists

We can use loop to Iterate Over a list, allowing operations to be performed on each element.

a = ['apple', 'banana', 'cherry']
for item in a:
    print(item)

apple
banana
cherry

Nested Lists

A nested list is a list that contains another list as its element. It is commonly used to represent matrices or tabular data. Nested elements can be accessed by chaining multiple indexes.

a = [[1, 2], [3, 4]]
print(a[0])
print(a[1][0])

[1, 2]
3

To know more, please refer to this article: List comprehension