This is a question about a program to determine whether a number is a prime number

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1

Could the following code be used to determine whether a number is prime? I’ve tested it and can’t find any exceptions.

Could the following code be used to determine a prime number?

def prime_checker(number):
   if number == 1:
     print("It's not a prime number.")
   if number % 2 == 0 or number % 3 == 0:
     print("It's not a prime number.")
   else:
    print("It's a prime number") ```
2 
>>> prime_checker(2)
It's not a prime number
>>> prime_checker(3)
It's not a prime number
>>> prime_checker(25)
It's a prime number
1 Like
3

I’m guessing you didn’t try huge numbers like… 25.

1 Like
4

A good way to check that code is working as intended, is to test it against a known outcome.

Prime numbers, for the most part, are well established and as such you can check your code against a list:

def prime_checker(number):
    if number == 1:
        return False
    if number % 2 == 0 or number % 3 == 0:
        return False
    else:
        return True


prime_list = [
    2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53,
    59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113,
    127, 131, 137, 139, 149, 151, 157, 163, 167, 173
]

for n in range(174):
    check = prime_checker(n)
    if check and n in prime_list:
        print(n, "checks out")
    elif check and n not in prime_list:
        print(n, "does not check out")
    elif not check and n in prime_list:
        print(n, "does not check out")

I’ve include the first 40 prime numbers and modified your function so that it returns True or False.

This is the output for zero to 25:

2 does not check out
3 does not check out
5 checks out
7 checks out
11 checks out
13 checks out
17 checks out
19 checks out
23 checks out
25 does not check out
...

As you can see, you’ve not nailed this, but you’re trying, so that’s no bad thing.

1 Like
5

Actually, I went bigger, like in the 900’s.

6

Thank you for both taking the time to answer and the encouragement! This was very helpful.

1 Like
7

Testing for primality is such a popular pastime at rowdy
mathematician parties that it has its own Wikipedia article, and
there are numerous other writeups about different approaches and
optimizations you can find all over the place. You might try picking
one of the simpler popular algorithms and working out how to codify
it, unless the point of the assignment is to find your own prime
number test algorithm.

I was about to link the Wikipedia article, and then realized it
contains an example in Python (a concise 11-line implementation), so
maybe avert your eyes if you read that one. Also be careful not to
accept party invites from mathematicians, no matter how innocent
they may seem!

9

This is a simple code which involves reconsidering the output by the code itself and providing a final output so that there will be no duplicated outputs.
If there is any simple way just lemme know :slight_smile:

n = int(input('enter number:'))
for i in range(2,n//2+1):
    if n%i == 0:
       from subprocess import run
       capture_output = True
       if capture_output == True:
           print('it is not a prime')
           break
else:
   print('it is a prime')

if n < 0:
    print('Only positive values can be executed')