Python prime number generator

[nickspacemonkey]

Hi guys,

I'm learning python and having a little trouble with my program.

It's supposed to generate the next prime number when the user hits enter. Instead it is just returning the odd numbers.

 

number = 5

def generate_prime(num):
    for i in range(2,num):
        if (num % i) == 0:
            num += 1
            generate_prime(num)
        return(num)

while True:
    input("Hit enter to get the next prime number.")
    print(generate_prime(number))
    number = generate_prime(number) + 1

 

I've looked at prime number check examples and the formula seems correct. Any pointers would be helpful as i'm stuck and a good hint might get me going.

 

Thanks.

[SCHISCHKA]

You have num +=1 which changes the value of num and you are returning that changed value; hence always odd.

change

18 minutes ago, nickspacemonkey said:

num += 1            

generate_prime(num)

to

18 minutes ago, nickspacemonkey said:

generate_prime(num + 1)

 

 

[SCHISCHKA]

you also have an additional +1 after the recursion

20 minutes ago, nickspacemonkey said:

    number = generate_prime(number) + 1

 

[SCHISCHKA]

one of those two above is correct. I'm not super familiar with python or generating primes

[polyx95]

Your method works but is incredibly slow for numbers > a few thousands. You should look into implementing https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes. 

[Niemand]

1 hour ago, polyx95 said:

You should look into implementing https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes. 

This is really cool.