Adding a number to the list if it passes the conditions in another function

Question

so I've written a function which checks if a number is a prime

def prime_checker(prime):
    limit = int(math.sqrt(prime))
    x = 2
    while x <= limit:
        if prime % x != 0:
            x += 1
            if x == limit:
                print("%d is prime" % prime)
                return True
        else:
            print("%d Not a prime" % prime)
            return False

prime_checker(199)

Now I want to create a function which tests numbers with prime_checker method and append this number to a list if it is prime. My attempt for it is:

def prime_counting():
    list_of_primes = []
    for x in range(10):
        if prime_checker(x) == True:
            list_of_primes.append(x)
    print(list_of_primes)

prime_counting()

However, this doesn't work. Is there any way to fix this?

`prime_checker(9)`, `prime_checker(25)`, `prime_checker(49)`, `prime_checker(121)` – what do these suggest about `limit`? — Ry-, Nov 22 '16 at 17:21
`prime_checker(3)` returns `None`. That seems like a good place to start debugging. — Kevin, Nov 22 '16 at 17:22
"However, this doesn't work. Is there any way to fix this?" -- There's almost certainly a way to fix it. The question is what is broken? Is there an exception? Is the output wrong? Are you sure that your `prime_checker` function is working correctly? etc. — mgilson, Nov 22 '16 at 17:23
your `prime_checker` can potentially have no return, I believe that is the current problem you are facing — depperm, Nov 22 '16 at 17:24
You might want to look at http://stackoverflow.com/questions/15285534/isprime-function-for-python-language to see why your prime checker is not correct? — Fallenreaper, Nov 22 '16 at 17:26

score 0 · Accepted Answer · answered Nov 22 '16 at 17:27

0

Your prime checker does not work in some cases. Try

def prime_checker(prime):
    limit = int(math.sqrt(prime))
    for x in range(2, limit + 1):
        if prime % x == 0:
            return False
    return True

answered Nov 22 '16 at 17:27

blue_note

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score 0 · Answer 2 · answered Nov 22 '16 at 17:37

You have almost done it correctly, there is only a minute (logical) error in the order of one of the statement.

def prime_checker(prime):
limit = int(math.sqrt(prime))
x = 2
while x <= limit:
    if prime % x != 0:
        if x == limit:
            print("%d is prime" % prime)
            return True
    x += 1
    else:
        print("%d Not a prime" % prime)
        return False

This is the updated prime_checker function. I have only found out your error. Otherwise your logic was absolutely correct. :)

Adding a number to the list if it passes the conditions in another function

2 Answers2