What is wrong with my Python Prime Number Finder code?

Question

Can you tell me why my fundamental Python program doesn't run properly. First I have a isprime module:

def isPrime(value): 
    count = 0
    for i in range(1, value + 1): 
        if value % i == 0: 
            count += 1
    if count == 2: 
        return True
    else: 
        return False

and I import it to the PrimeFinder.py:

from isPrime import isPrime
lst = []
NumberOfValue = int(input())
for i in range(1, NumberOfValue + 1): 
    value = int(input())   
    lst.append(value)
for value in lst:
    if isPrime(value) == False: 
        lst.remove(value)
print(lst)

But when I input: the result also include non-prime numbers, can you explain if I was wrong in somewhere, thanks a lot for you help

for prime numbers, you need to find mod of i till values//2. For example to find if 17 is prime, you dont have to go all the way to 16. You just need to check between 2 and 8. Any value beyond 8 will result in 0.x — Joe Ferndz, Jan 07 '21 at 06:18
You are trying to edit a list while iterating through it. This is discouraged. Take a look at the `filter` function as an alternative. — M Z, Jan 07 '21 at 06:19
Why are you appending any number to the list instead of checking them beforehand? — OneCricketeer, Jan 07 '21 at 06:19
'cause of this line `lst.remove(value)`. Don't mutate the list while iterating. Small example `a = [1, 2]; for i in a: a.remove(i)` now `a` would still be `[2]`. — Ch3steR, Jan 07 '21 at 06:19

score 0 · Answer 1 · answered Jan 07 '21 at 06:21

0

from isPrime import isPrime
lst = []
NumberOfValue = int(input())
for i in range(1, NumberOfValue + 1): 
    value = int(input())   
    if isPrime(value):
        lst.append(value)
print(lst)

Change the code to this, it will work. .remove will not remove the value from the list

answered Jan 07 '21 at 06:21

SAI SANTOSH CHIRAG

2,046
1
10
26

thank for you help, I appreciate that – Digital Cat Jan 07 '21 at 06:26

score 0 · Answer 2 · answered Jan 07 '21 at 06:22

Appears you should be doing

for i in range(1, NumberOfValue + 1): 
    value = int(input())   
    if isPrime(value):
        lst.append(value)

Otherwise, you're modifying a list while iterating, and therefore skipping over some indicies and leaving elements behind

Regarding the efficiency of your isPrime function, there are better ways isPrime Function for Python Language

What is wrong with my Python Prime Number Finder code?

2 Answers2