for Loops in Nested Lists

In Python, nested lists (lists within lists) are often used to store structured data, like tables. When working with such data, for loops help iterate through each sublist and its elements efficiently.

Using a Nested for Loop

A nested for loop is simply a loop inside another loop. The outer loop iterates through the main list, while the inner loop iterates through each sublist.

Example: Iterating Over a Nested List

students = [
    ["Alice", 85],
    ["Bob", 78],
    ["Charlie", 92]
]

for student in students:  # Outer loop: iterates through sublists
    for data in student:  # Inner loop: iterates through elements in sublists
        print(data, end=" ")  # Print elements on the same line
    print()  # New line after each sublist

Output

Alice 85  
Bob 78  
Charlie 92  

Accessing Elements Using Indexes

Instead of looping over sublists directly, you can access elements using indexes.

for student in students:
    name = student[0]  # First element is the name
    score = student[1]  # Second element is the score
    print(f"{name} scored {score}")

Output

Alice scored 85  
Bob scored 78  
Charlie scored 92  

Adding Conditions in Nested Loops

You can add if statements inside a loop to filter data. For example, printing only students who scored 80 or higher:

for student in students:
    name = student[0]
    score = student[1]
    if score >= 80:  # Condition to check high scores
        print(f"{name} passed with {score}")

Output

Alice passed with 85  
Charlie passed with 92  

Exercise: Try It Yourself!

1. Create a nested list containing the names of students and their test scores.
2. Use a nested loop to print each student's name and score.
3. Modify your loop to print only students who scored 80 or higher.

Example:

grades = [
    ["Jake", 76],
    ["Lily", 89],
    ["Tom", 95],
    ["Emma", 67]
]

# Your loop here