sieve exercise adapted for python

EXERCISES.txt

@@ -15,6 +15,7 @@ grains
 gigasecond
 triangle
 scrabble-score
+sieve
 roman-numerals
 binary
 prime-factors

sieve/example.py

@@ -0,0 +1,13 @@
+def sieve(limit):
+    primes = []
+
+    sv = [True] * limit
+    sv[:2] = [False, False]     # 0 and 1 aren't prime
+
+    for n in range(limit):
+        if sv[n]:  # n is prime
+            for i in range(n * 2, limit, n):    # mark all multiples of n
+                sv[i] = False
+            primes.append(n)
+
+    return primes

sieve/sieve_test.py

@@ -0,0 +1,20 @@
+try:
+    from sieve import sieve
+except ImportError:
+    raise SystemExit('Could not find sieve.py. Does it exist?')
+
+
+import unittest
+
+
+class SieveTest(unittest.TestCase):
+    def test_a_few_primes(self):
+        expected = [2, 3, 5, 7]
+        self.assertEqual(expected, sieve(10))
+
+    def test_primes(self):
+        expected = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503, 509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599, 601, 607, 613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691, 701, 709, 719, 727, 733, 739, 743, 751, 757, 761, 769, 773, 787, 797, 809, 811, 821, 823, 827, 829, 839, 853, 857, 859, 863, 877, 881, 883, 887, 907, 911, 919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997]
+        self.assertEqual(expected, sieve(1000))
+
+if __name__ == '__main__':
+    unittest.main()