debian :: ~ % python
Python 2.7.9 (default, Mar  1 2015, 12:57:24)
[GCC 4.9.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from math import sqrt
>>> def isPrime(x):
...   # Naive algorithm
...   if x<=1 : return False
...   if x==2: return True
...   if x%2==0: return False
...   for i in xrange( 3, int(sqrt(x))+1, 2 ):
...     if x%i==0:
...       return False
...   return True
...
>>> isPrime( 5) and isPrime(11)
True
>>>