I get "Your function fails on is_prime(4). It returns None when it should return False."

Unless I'm missing something, this code should divide 4 / 2 and find it's not a prime. I don't understand why it returns "None".

```
#Define a function called is_prime that takes a number x as input.
#For each number n from 2 to x - 1, test if x is evenly divisible by n.
#If it is, return False.
#If none of them are, then return True.
x=raw_input("Number?")
x=int(x)
def is_prime(x):
if x==1 or x==0:
return False
if x==2 or x==3:
return True
if x>3:
for n in range(2, x-1):
if x % n == 0:
return False
else:
return True
is_prime(x)
```