Python Lists Explained (With Examples, Slicing & Methods)

What Is a List in Python?

A list is a collection used to store multiple values in a single variable.

Key Characteristics of Lists

• Ordered (items have a fixed position)
• Mutable (can be changed after creation)
• Allows duplicate values
• Can store mixed data types

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Creating a List in Python

Let’s start with a simple example: a list of student marks.

marks = [94.4, 87.5, 95.2, 66.4, 45.1]

print("Marks:", marks)
print("Type of marks:", type(marks))
print("Total number of marks:", len(marks))

Explanation:

• The list stores float values
• type() confirms it is a list
• len() gives the number of elements

Output:

<class 'list'>
5

Accessing List Elements Using Index

Python lists use zero-based indexing, meaning the first element starts at index 0.

print("First mark:", marks[0])
print("Second mark:", marks[1])

Important Tip:

Trying to access an index that does not exist will cause an IndexError.

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Lists Can Store Mixed Data Types

Unlike some languages, Python allows lists to store different data types together.

student = ["Nishi", 96.7, 17, "Delhi"]
print("Student details:", student)

Updating List Values (Mutability)

Lists are mutable, meaning you can change their content.

student[0] = "Nishtha"
print("Updated student name:", student[0])

This is a major advantage of lists over strings.

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Another Example: List of Integer Marks

student_marks = [59, 89, 58, 70, 90]
print("Original student marks:", student_marks)

This list stores only integer values and is commonly used in real projects like result processing.

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List Slicing in Python

Slicing allows you to extract a portion of a list.

Syntax

list[start : end]   # end index is excluded

Examples from the Code

print("Marks from index 1 to end:", student_marks[1:])
print("Marks from start to index 3:", student_marks[:4])
print("Marks from index -3 to -2:", student_marks[-3:-1])

Explanation:

• student_marks[1:] → from index 1 till the end
• student_marks[:4] → from start to index 3
• Negative indexing starts from the end of the list

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Commonly Used List Methods in Python

Python provides powerful built-in methods to work with lists efficiently.

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append() – Add Element at the End

student_marks.append(95)

Adds a new value at the end of the list.

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sort() – Sort the List

student_marks.sort()

Sorts the list in ascending order.

student_marks.sort(reverse=True)

Sorts the list in descending order.

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reverse() – Reverse the List Order

student_marks.reverse()

Reverses the current order of elements.

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insert(index, value) – Insert at Specific Position

student_marks.insert(2, 43)

Inserts 43 at index 2 without removing existing elements.

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pop(index) – Remove Element by Index

student_marks.pop(2)

Removes and returns the element at index 2.

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Difference Between Strings and Lists in Python

This is a very common interview and beginner confusion, so let’s clear it properly.

Feature	String	List
Data Type	Text (characters)	Collection of values
Mutable	❌ No	✅ Yes
Indexing	✅ Yes	✅ Yes
Slicing	✅ Yes	✅ Yes
Modification	❌ Not allowed	✅ Allowed
Example	"Python"	["P", "y", "t", "h", "o", "n"]

Example Difference

# String (immutable)
name = "Python"
# name[0] = "J"  ❌ Error

# List (mutable)
letters = ["P", "y", "t", "h", "o", "n"]
letters[0] = "J"  # ✅ Allowed

Key takeaway:

• Use strings for text that should not change.
• Use lists when data needs to be updated or manipulated.

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When Should You Use Lists?

• Storing marks, prices, scores
• Managing user data
• Handling collections of items
• Working with dynamic data

In real-world Python applications, lists are used everywhere from web apps to data science.

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Happy Learning !