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

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