```
def is_prime(x):
if x < 2 :
return False
elif x ==2:
return True
else:
for n in range(2, x-1):
if x % n == 0:
return False
```

There always something wrong: "Oops, try again. Your function fails on is_prime(3). It returns None when it should return True."

Can anyone help me with that? Thanks!

```