Why is my Python prime number checker not working?

Question

Why is my code below giving me wrong results? When I give it numbers like 2 and 3, it says they’re not prime numbers. Only some numbers work but for the most part it gives wrong answers.

def prompt_input(input_msg, error_msg):
    while True:
        userinput = input(input_msg)
        try:
            integer = int(userinput)
            if integer > 1:
                return integer
            print(error_msg)
        except ValueError:
            print(error_msg)
    
def check_prime(number):
    for i in range(2, number):
        if number % i == 0:
            return False   
        return True

primenum = prompt_input(
    "Give an integer that's bigger than 1: ",
    "You had one job"
)

if check_prime(primenum):
    print("This is a prime.")
else:
    print("This is not a prime.")

Asked By: Aleksi Vuorinen

||

Source

Answer 1

First issue: Your for loop returns after one iteration, so the correct return logic would be:

def check_prime(number):
    for i in range(2, number):
        if number % i == 0:
            return False   
    return True

However you are implementing this incorrectly as well, the loop needs to iterate up to the sqrt of the number.

def check_prime(number):
    for i in range(2, int(sqrt(number))+1):
        if number % i == 0:
            return False   
    return True

Hope this helps!

Answered By: Dennis Afanasev

Answer 2

Need to unindent the return True.

def check_prime(number):
    for i in range(2, number):
        if number % i == 0:
            return False   
    return True

Answered By: zerocog

Why is my Python prime number checker not working?

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