Rahul Gupta

Posted on Jul 10

Day 21/100: Lists in Python – Create, Access, Modify

#python #programming #learning #100daysofcode

Welcome to Day 21 of the 100 Days of Python series!
Today we’re diving into one of Python’s most useful and versatile data types — the list.

Lists are ordered, changeable, and allow duplicate values. They’re your go-to structure for storing collections like user names, scores, tasks, or pretty much anything.

📦 What You’ll Learn

How to create a list
How to access list elements
How to modify items
Common use cases and tips

Let’s get started! 🐍

🔹 1. Creating a List

Lists are created using square brackets [].

# Empty list
empty = []

# List of strings
fruits = ["apple", "banana", "cherry"]

# Mixed data types
info = ["Alice", 30, True]

You can also create a list from a string or range:

list_from_str = list("hello")        # ['h', 'e', 'l', 'l', 'o']
list_from_range = list(range(5))     # [0, 1, 2, 3, 4]

🔹 2. Accessing List Elements

Use indexing to access items. Indexes start at 0.

fruits = ["apple", "banana", "cherry"]
print(fruits[0])   # apple
print(fruits[-1])  # cherry (last item)

Access a Range of Items – Slicing

fruits = ["apple", "banana", "cherry", "date"]
print(fruits[1:3])   # ['banana', 'cherry']
print(fruits[:2])    # ['apple', 'banana']
print(fruits[2:])    # ['cherry', 'date']

🔹 3. Modifying List Items

Lists are mutable, meaning you can change their contents.

Replace an Item

fruits[1] = "blueberry"
print(fruits)  # ['apple', 'blueberry', 'cherry']

Add Items

fruits.append("date")             # Add to end
fruits.insert(1, "kiwi")          # Insert at index 1

Remove Items

fruits.remove("banana")  # Remove by value
fruits.pop()             # Remove last item
del fruits[0]            # Remove by index

Clear All Items

fruits.clear()  # Now an empty list

🔹 4. Check Membership

if "apple" in fruits:
    print("Yes, apple is in the list")

🔹 5. Get Length of a List

print(len(fruits))  # Number of items in the list

🔹 6. Nested Lists

Lists can contain other lists (2D or more):

matrix = [
    [1, 2],
    [3, 4]
]

print(matrix[1][0])  # 3

🔹 7. Loop Through a List

for fruit in fruits:
    print(fruit)

Use enumerate() to get index + value:

for index, fruit in enumerate(fruits):
    print(index, fruit)

🔹 8. Copy a List

copy1 = fruits.copy()
copy2 = fruits[:]  # Slice syntax

Avoid copy = fruits – it just creates a reference.

💡 Pro Tip: Heterogeneous Lists Are Allowed

Lists can contain anything — even functions, objects, or other lists:

mixed = [42, "hello", [1, 2], True, len]

🧠 Recap

Today you learned:

How to create and initialize lists
How to access and slice items using indexing
How to add, change, or remove items
Tips on copying, looping, and nested lists

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