How to Print Rectangles with Nested Loops in Python

This guide explains how to use nested loops in Python to print a rectangle of characters (like asterisks) to the console. We'll cover the basic logic and how to create a reusable function.

Basic Rectangle Printing with Nested Loops

The core concept is to use two nested for loops:

• The outer loop controls the rows.
• The inner loop controls the columns (characters within each row).

num_rows = 2
num_cols = 3

for _ in range(num_rows):       # Outer loop: rows
    for _ in range(num_cols):   # Inner loop: columns
        print('*', end=' ')     # Print an asterisk and a space
    print()                     # Move to the next line after each row

Output:

* * *
* * *

• for _ in range(num_rows):: This loop iterates num_rows times. We use _ as the loop variable because we don't actually need the loop counter value itself, just the repetition.
• for _ in range(num_cols):: This inner loop iterates num_cols times for each row. Again, we use _ because we don't need the counter.
• print('*', end=' '): This prints an asterisk followed by a space. The end=' ' is crucial; it prevents print() from adding a newline, so the asterisks for a single row stay on the same line.
• print(): This empty print() statement adds a newline after each row has been printed. Without this, you'd get all the asterisks on a single line.

Creating a Reusable Function

It's good practice to encapsulate this logic in a function:

def print_rectangle(num_rows, num_cols):
    for _ in range(num_rows):
        for _ in range(num_cols):
            print('*', end=' ')
        print()  # Newline after each row

print_rectangle(2, 3)
print()
print_rectangle(3, 4)
print()
print_rectangle(4, 5)

Output:

* * *
* * *

* * * *
* * * *
* * * *

* * * * *
* * * * *
* * * * *
* * * * *

• The function now takes num_rows and num_cols as arguments, making it reusable for different rectangle sizes.
• The logic inside the function is identical to the previous example.