Add function to list primes

src/Python/utils.py

@@ -16,11 +16,29 @@ def timeit(name):
     return profile
 
 
-
 def is_prime(n):
     if n % 2 == 0 and n > 2:
         return False
     for i in range(3, int(math.sqrt(n)) + 1, 2):
         if n % i == 0:
             return False
-    return True
+    return True
+
+
+# Returns a list of True and False indicating whether each number is prime.
+# For 0 <= i <= n, result[i] is True if i is a prime number, False otherwise.
+def list_primality(n):
+    # Sieve of Eratosthenes
+    result = [True] * (n + 1)
+    result[0] = result[1] = False
+    for i in range(int(math.sqrt(n) + 1)):
+        if result[i]:
+            for j in range(i * i, len(result), i):
+                result[j] = False
+    return result
+
+
+# Returns all the prime numbers less than or equal to n, in ascending order
+# For example: list_primes(97) = [2, 3, 5, 7, 11, ..., 83, 89, 97].
+def list_primes(n):
+    return [i for (i, is_prime) in enumerate(list_primality(n)) if is_prime]