How to Check If a Number Is Even in Python

Checking if a number is even or odd is one of the most fundamental tasks in programming. An even number is an integer that is divisible by 2 without a remainder (e.g., 2, 4, 6, 0, -2). Conversely, an odd number leaves a remainder of 1 (e.g., 1, 3, 5).

This guide explains how to use the modulo operator % for standard checks and touches on bitwise operations for high-performance scenarios.

Method 1: Using the Modulo Operator (Standard)

The modulo operator % returns the remainder of a division. For any integer n, n % 2 will be 0 if even, and 1 (or -1 in some languages, though Python handles negative modulo consistently as 1) if odd.

Example:

number = 10

if number % 2 == 0:
    print(f"{number} is Even")
else:
    print(f"{number} is Odd")

Output:

10 is Even

Handling Negative Numbers

Python's modulo operator handles negative numbers gracefully for parity checks. -4 % 2 is 0, so it is correctly identified as even.

Method 2: Using Bitwise AND (Optimized)

For extremely high-performance loops, you can use the bitwise AND operator &. In binary, even numbers always end with a 0 bit (e.g., 2 is 10, 4 is 100), while odd numbers end with a 1 bit.

Performing number & 1 checks only the last bit.

• If number & 1 is 0: Even
• If number & 1 is 1: Odd

number = 7

if (number & 1) == 0:
    print(f"{number} is Even")
else:
    print(f"{number} is Odd")

Output:

7 is Odd

Method 3: Checking Floating Point Numbers

The concept of "even" usually applies to integers. However, if you have a float like 4.0, you might want to treat it as even.

A float 4.0 % 2 returns 0.0. A float 4.5 % 2 returns 0.5.

num_float = 4.0

if num_float % 2 == 0:
    print(f"{num_float} is effectively even.")
else:
    print(f"{num_float} is not even.")

Output:

4.0 is effectively even.

Common Pitfall: String Inputs

Users input data as strings (e.g., from input()). Performing arithmetic on strings raises a TypeError.

user_input = "10"

try:
    if user_input % 2 == 0:
        print("Even")
except TypeError as e:
    print(f"Error: {e}")

if int(user_input) % 2 == 0:
    print("Even (after conversion)")

Output:

Error: not all arguments converted during string formatting
Even (after conversion)

Conclusion

To check if a number is even:

1. Use num % 2 == 0 for the standard, readable approach.
2. Use (num & 1) == 0 for bitwise operations (advanced).
3. Convert inputs using int() before checking to avoid TypeErrors.