Here you will get python program to check prime number.

A number is called prime number if it is only divisible by 1 or itself. For example 2, 3, 5, 7, 11, etc are prime numbers.

Below program takes a number as input and checks it is prime number or not.

## Python Program to Check Prime Number

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num = int(input("enter a number: ")) for i in range(2, num): if num % i == 0: print("not prime number") break else: print("prime number") |

**Output**

*enter a number: 11*

*prime number*

Comment below if you have any queries related to above python prime number program.

Here according to the program else is inside the for loop. When the if condition fails, directly it will print as the number is not prime until checking up to the last value. If I take num=9, then in first iteration (9%2)==0 (false) else statement will be executed. But 9 is not prime right. can u explain me this prgm.

See, this else is not the part of if. In python for loop is little different from other languages like C and C++. In python we can use a else statement with for loop. After the loop ends, else statement is executed. In case break is used somewhere in loop then else is not executed. The program is correct and works fine, just try to run it.

You can learn about for loop in python here https://www.programiz.com/python-programming/for-loop

def prime_check(number= ‘Plese enter a valid number’):

for s in range(2,number+1):

if number<=1 or number / s != 0:

print("it's not a prime number")

else:

print("It's a prime number")

return

Sir I can check as below also.

I am mentioning the logic here only

initialize i to 2

Store the number to be checked at n

now I will check for every i that whether it divides n or not;and the loop will continue till i reaches n

if for any value of i it divides n,n will be non-prime and if no value of i can divide n then n will be prime.

Sir I cannot fully apply the idea in my program.Will you please help me ASAP?

sir ur program gives an error while we entering greater than 10 .this error only occur when we enter prime number ..

thanks brother , my program doesn’t runs because i doesn’t put the break statement at end of loop.

for i in range(2,30):

j=2

while j<i:

if i%j==0:

j=j+1

break

else:

print("%s it is prime"%(i))

j=j+1

break

def primes(num):

list=[]

for i in range (2,int(num/2)+1):

if ((num%i)==0):

break

else:

list.append(i)

return list

primes(11)

iam unable to append primes to list please help me out

It returns a list of primes upto a number n.

def primes_upto(n):

arr = []

for i in range(1, n+1):

if i in [2, 3]:

arr.append(i)

continue

for j in range (2, (i//2) + 1):

if i % j == 0:

break

if j == i//2:

arr.append(i)

return arr

This program has a small error. This works fine for other inputs except for 4. It says 4 is a prime number which is actually not.

When input is 4, range function is range(2, 2). This returns an empty list. Thus the execution is jumped to else block. And, it prints ‘prime number’.

Hence, it should be range(2, int(n/2) + 1) instead of range(2, int(num/2)).

This corrects the error!

Thanks for pointing out mistake, I have corrected it.

When the chosen number is 2, how does it not print anything from the if statement when 2%2 is 0. I am confused.

As the function range(2,var) will produce list of numbers from 2 up to var.i.e. 1 less than var. so in the case var=2,

range(2,2) produces EMPTY LIST. And thus 2 never gets break statement.

1 is not a prime but this program never considered that.