Alternating Odd/Even Rows Number Pattern in Python

Beginner
⏱️ 7 min read
📚 Updated: Aug 2025
🎯 2 Code Examples
Conditionals
Alternating odd/even rows number pattern output (1, 2 4, 1 3 5, 2 4 6 8, 1 3 5 7 9) in Python programming

What You’ll Learn

How to print an alternating odd/even rows number pattern in Python using nested loops and an if condition. Odd rows print odd numbers and even rows print even numbers.

This is a great exercise for combining conditionals with step-based ranges.

⭐ Pattern Output

For rows = 5, the pattern looks like this:

Output
1
2 4
1 3 5
2 4 6 8
1 3 5 7 9
1

Complete Python Program

Use i % 2 to choose whether to print odd or even numbers on each row.

Python
rows = 5

for i in range(1, rows + 1):
    if i % 2 == 0:
        for j in range(2, 2 * i + 1, 2):
            print(j, end=" ")
    else:
        for j in range(1, 2 * i, 2):
            print(j, end=" ")
    print()

🧠 How It Works

1

Decide the number of rows

rows = 5 prints 5 lines of output.

Setup
2

Outer loop picks the row index

for i in range(1, rows + 1) runs i = 1..5.

Row control
3

If i is even, print even numbers

For even rows, we print 2, 4, 6, ... up to 2*i using range(2, 2*i + 1, 2).

Even rows
4

If i is odd, print odd numbers

For odd rows, we print 1, 3, 5, ... up to 2*i - 1 using range(1, 2*i, 2).

Odd rows
=

Alternating odd/even rows

A single parity check creates two different sequences per row, producing the alternating effect.

2

Variation — User Input Version

Let the user choose the number of rows at runtime:

Python
rows = int(input("Enter the number of rows: "))

for i in range(1, rows + 1):
    if i % 2 == 0:
        for j in range(2, 2 * i + 1, 2):
            print(j, end=" ")
    else:
        for j in range(1, 2 * i, 2):
            print(j, end=" ")
    print()

💡 Tips for Enhancement

Try These

  • Remove trailing spaces by building each row as a list and joining it
  • Swap the rule so odd rows print evens and even rows print odds
  • Print squares/cubes of numbers instead of raw values
  • Right-align the pattern by printing leading spaces
  • Use the same logic to alternate other sequences (primes, Fibonacci, etc.)

Avoid

  • Forgetting the step value of 2 in the inner ranges
  • Using the wrong end value in range() (stop is exclusive)
  • Assuming user input is always valid
  • Mixing up the even/odd branch logic

Key Takeaways

1

A parity check (i % 2) decides which sequence to print.

2

Even rows print evens up to 2*i; odd rows print odds up to 2*i - 1.

3

Step-based ranges (step=2) make odd/even sequences easy.

4

This is a simple example of combining conditionals with nested loops.

❓ Frequently Asked Questions

Because the code uses end=" " to print a space after each value. You can remove trailing spaces by joining a list instead.
Yes. Change end=" " to end="". For readability, spaces are usually better.
Swap the branches: print odds in the even branch and evens in the odd branch.
O(n²) for n rows because the total printed values form a triangular count.

Explore More Python Number Patterns!

From simple triangles to alternating sequences—keep practicing nested loops and conditionals.

All Number Patterns →
Did you know?

Odd and even sequences can be generated without conditionals by choosing the right range(): odds use range(1, n, 2) and evens use range(2, n, 2).

About the author

Mari Selvan M P
Mari Selvan M P 🔗

Developer, cloud engineer, and technical writer

  • Experience 12 years building web and cloud systems
  • Focus Full Stack Development, AWS, and Developer Education

I write practical tutorials so students and working developers can learn by doing—from databases and APIs to deployment on AWS.

AWS Certified Developer – Associate (Credly)

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