python program to check for prime number

In this post, you will learn a python program to check given number is prime or not but before writing a program we should know what is a prime number.

What is prime number?

A number that is only divisible by 1 and itself is known as a prime number. An example of a prime number is 2,3,5,7,11,13,17,19… etc.

we should write this program in three different ways:

1. Simple way (By taking user input).
2. by using function.
3. Except error if user enter wrong input.

1. Simple way (By taking user input)

Write a python program to check given number is prime or not by taking user input.

Before writing this program you should know about:

1. if-else
2. for loop

Source Code

num = int(input("enter a number to check entered number is prime or no :"))
p = 0
print(f"{num} is divide by :",end=" ")
for i in range(2,num):
    if num%i==0:
        print(i, end=",")
        p=1
print("\t")
if p==1 and num!=2:
    print(f"{num} is not a prime number")
else:
    print(f"{num} is a prime number")

Output-1

enter a number to check entered number is prime or no :4
4 is divide by : 2,
4 is not a prime number

Output-2

enter a number to check entered number is prime or no :2
2 is divide by : 
2 is a prime number

Explanation

num variable is used to take integer value as input from the user.

p variable (which is initially 0) is used to check for prime numbers when p=1 which means that num is not a prime number.

with the help of for loop and if statement we check for num is divisible by any other number (Except 1 or num ) or not, if a number is divisible by any other number then p=1 that shows num is not a prime number.

2. prime number By using function

Write python program to check given number is prime or not using function.

Before writing this program you should know about:

1. if-else
2. for loop
3. function

Source Code

def prime_number(n):
    check_prime = 0
    for i in range(2,n):
        if n%i == 0:
            check_prime = 1
    if check_prime == 1:
        return f'{n} is not a prime number'
    else:
        return f'{n} is a prime number'

# you can also take user input instead of writing direct value
# user input - demo
# num1 = int(input("ENter a number: "))
# prime_number(num1)

print(prime_number(2))
print(prime_number(4))
print(prime_number(5))
print(prime_number(6))
print(prime_number(7))
print(prime_number(9))

Output

2 is a prime number
4 is not a prime number
5 is a prime number
6 is not a prime number
7 is a prime number
9 is not a prime number

3. Except error if user enter wrong input.

Write a python program to check given number is prime number or not and also handle exception if user input wrong data.

before writing this program you should know about:

1. if-else
2. for loop
3. while loop
4. try-except block

Source code

def prime_number(n):
    check_prime = 0
    for i in range(2,n):
        if n%i == 0:
            check_prime = 1
    if check_prime == 1:
        return f'{n} is not a prime number'
    else:
        return f'{n} is a prime number'

while True:
    try:
        number = int(input("Enter a number: "))
        if type(number) == int:
            break
    except ValueError:
        print("please enter number only")

print(prime_number(number))    

Output-1

Enter a number: seven
please enter number only
Enter a number: 7
7 is a prime number

Output-2

Enter a number: four
please enter number only
Enter a number: 4
4 is not a prime number

Hope this post help you and add good value to your life -thank you.