python - Function testing for primes not working as needed -

it's supposed find out if given input prime number or not.

def is_prime(x):     if x <= 1:         return false     elif x == 2 or x == 3:         return true     else:         n in range(2, x-1):             if x % n == 0:                 return false             else:                 return true 

but

is_prime(9) 

gives true should return false.

i can't find bug, need help.

you return true moment find factor doesn't divide x evenly. 2 doesn't divide 9 return true then:

>>> x = 9 >>> n = 2 >>> if x % n == 0: ...     print false ... else: ...     print true ...  true 

you need return true when determined no factors exist, outside loop:

for n in range(2, x-1):     if x % n == 0:         return false return true 

you don't need test x - 1, testing int(x ** 0.5) + 1 enough (so square root):

def is_prime(x):     if x <= 1:         return false     if x in (2, 3):         return true     n in range(2, int(x ** 0.5) + 1):         if x % n == 0:             return false     return true