Updated sieve of erathostenes function

Previous Code was not working, so i changed xrange to range (so the code could work on both  python2 and python3).
In one of the For loop the upper bound of range was not an integer, so changed it to integer.
And for index 0 and 1 primes list need to be set to False.

Author: varsubham

primelib/primelib.py

@@ -100,15 +100,16 @@ def sieveEr(N):
     # precondition
     assert isinstance(N, int) and (N > 2), "'N' must been an int and > 2"
 
-    primes = [True for x in xrange(N + 1)]
+    primes = [True for x in range(N + 1)]
 
-    for p in xrange(2, sqrt(N) + 1):
+    for p in range(2, int(sqrt(N)) + 1):
         if (primes[p]):
-            for i in xrange(p*p, N + 1, p):
+            for i in range(p*p, N + 1, p):
                 primes[i] = False
-
+    primes[0]=False
+    primes[1]=False
     ret = []
-    for p in xrange(N + 1):
+    for p in range(N + 1):
         if primes[p]:
             ret.append(p)