Thursday, October 31, 2019

Python Program to Display Prime Numbers

In this post we'll see a Python program to display prime numbers in the given range. This program helps in understanding usage of nested loops and it also shows a use case where for loop with else in Python can be used.

A number is a prime number if it can be divided either by 1 or by the number itself. So every number with in the given range has to be divided in a loop from 2 till number/2 to check if number is a prime number or not. You only need to run your loop from 2 to N/2 (where N is the current number in the passed range), as no number is completely divisible by a number more than its half. Reducing the iteration to N/2 makes your program to display prime numbers more efficient.

Displaying prime numbers Python program

def display_prime(lower, upper):
    for num in range(lower, upper+1):
        # instead of int(num/2), num//2 (floor division) can also be used
        for i in range(2, int(num/2)+1):
            # if number is completely divisible then it
            # it is not a prime number so break out of loop
            if num % i == 0:
        # if loop runs completely that means a prime number

def get_input():
    """Function to take user input for display range"""
    start = int(input('Enter start number for displaying prime numbers:'))
    end = int(input('Enter end number for displaying prime numbers:'))
    # prime numbers start from 2
    if start <= 1:
        start = 2
    # call function to display prime numbers
    display_prime(start, end)

# start program


Enter start number for displaying prime numbers:40
Enter end number for displaying prime numbers:100

That's all for this topic Python Program to Display Prime Numbers. If you have any doubt or any suggestions to make please drop a comment. Thanks!

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