diff -r 8fb3a6f9b0a4 Lib/random.py
--- a/Lib/random.py	Mon Aug 26 14:05:19 2013 +0200
+++ b/Lib/random.py	Mon Aug 26 19:07:11 2013 -0400
@@ -43,6 +43,8 @@
 from os import urandom as _urandom
 from collections.abc import Set as _Set, Sequence as _Sequence
 from hashlib import sha512 as _sha512
+from itertools import accumulate as _accumulate
+from bisect import bisect as _bisect
 
 __all__ = ["Random","seed","random","uniform","randint","choice","sample",
            "randrange","shuffle","normalvariate","lognormvariate",
@@ -246,14 +248,43 @@
 
 ## -------------------- sequence methods  -------------------
 
-    def choice(self, seq):
-        """Choose a random element from a non-empty sequence."""
-        try:
-            i = self._randbelow(len(seq))
-        except ValueError:
-            raise IndexError('Cannot choose from an empty sequence')
+    def choice(self, seq, weights=None):
+        """Choose a random element from a non-empty sequence.
+
+        Optional argument weights is a list of non-negative numbers used to 
+        alters the probability that element at index i in the sequence is 
+        selected.
+        """
+
+        if not weights:
+            try:
+                i = self._randbelow(len(seq))
+            except ValueError:
+                raise IndexError('Cannot choose from an empty sequence')
+            return seq[i]
+
+        # weights argument supplied
+        def _add(cumulative, partial):
+            try:
+                partial = float(partial)
+            except ValueError:
+                raise TypeError("All weights must be numeric")
+            if partial < 0:
+                raise ValueError("All weights must be non-negative")
+            return cumulative + partial
+
+        cumulative_dist = list(_accumulate(weights, _add))
+
+        if len(weights) != len(seq):
+            raise ValueError("Length of weights must equal length of sequence")
+
+        if not any(weights):
+            raise ValueError("At least one weight must be greater than zero")
+
+        x = self.random() * cumulative_dist[-1]
+        i = _bisect(cumulative_dist, x)
         return seq[i]
-
+            
     def shuffle(self, x, random=None, int=int):
         """Shuffle list x in place, and return None.
 
diff -r 8fb3a6f9b0a4 Lib/test/test_random.py
--- a/Lib/test/test_random.py	Mon Aug 26 14:05:19 2013 +0200
+++ b/Lib/test/test_random.py	Mon Aug 26 19:07:11 2013 -0400
@@ -96,6 +96,11 @@
             choice([])
         self.assertEqual(choice([50]), 50)
         self.assertIn(choice([25, 75]), [25, 75])
+        self.assertIn(choice([25, 75], [.25, .75]), [25, 75])
+        self.assertRaises(ValueError, choice, [25, 75], [.25])
+        self.assertRaises(ValueError, choice, [25, 75], [-1, -2])
+        self.assertRaises(ValueError, choice, [25, 75], [0, 0])
+        self.assertRaises(TypeError, choice, [25, 75], ['str1', 'str2'])
 
     def test_sample(self):
         # For the entire allowable range of 0 <= k <= N, validate that