Write a Program to check if a number is prime in Python

To check if a number is prime in Python, you need to verify if it has no divisors other than 1 and itself (excluding 1 and the number itself). Here's how you can write a Python program to check for prime numbers:

def is_prime(num):
    # Prime numbers are greater than 1
    if num <= 1:
        return False
    
    # Check for factors from 2 to sqrt(num)
    for i in range(2, int(num**0.5) + 1):
        if num % i == 0:
            return False
    
    return True

Explanation:

• The function is_prime(num) takes an integer num as input and returns True if num is a prime number, and False otherwise.

• Edge case: Numbers less than or equal to 1 are not prime (num <= 1).

• Prime number definition: Prime numbers are greater than 1 and have no divisors other than 1 and itself.

• Efficient checking: The loop runs from 2 to the square root of num (int(num**0.5) + 1). This is because, if num is divisible by any number greater than its square root, the corresponding factor would necessarily be less than its square root.

• Divisibility check: For each number i in the range, if num is divisible by i (num % i == 0), then num is not prime (return False).

Example Usage:

You can test the is_prime function with different numbers:

num1 = 17
num2 = 24
num3 = 2

print(f"Is {num1} prime? {is_prime(num1)}")  # Output: True
print(f"Is {num2} prime? {is_prime(num2)}")  # Output: False
print(f"Is {num3} prime? {is_prime(num3)}")  # Output: True

In the example above:

• num1 (17) is a prime number.
• num2 (24) is not a prime number (divisible by 2, 3, 4, 6, 8, 12).
• num3 (2) is a prime number.

This function efficiently checks whether a given number is prime using a simple iterative approach with a time complexity of $O(\sqrt{n})$, which is efficient for most practical purposes.