diff -r 9b7b8b7ccf28 Lib/fractions.py
--- a/Lib/fractions.py	Sat Oct 12 23:16:32 2013 +0200
+++ b/Lib/fractions.py	Sat Oct 12 22:22:42 2013 +0100
@@ -10,7 +10,7 @@
 import re
 import sys
 
-__all__ = ['Fraction', 'gcd']
+__all__ = ['Fraction', 'gcd','lcm']
 
 
 
@@ -24,6 +24,14 @@
         a, b = b, a%b
     return a
 
+def lcm(a, b):
+    """Calculate the Least Common Multiple of a and b."""
+    return a * b // gcd(a,b)
+
+
+
+
+
 # Constants related to the hash implementation;  hash(x) is based
 # on the reduction of x modulo the prime _PyHASH_MODULUS.
 _PyHASH_MODULUS = sys.hash_info.modulus
diff -r 9b7b8b7ccf28 Lib/test/test_fractions.py
--- a/Lib/test/test_fractions.py	Sat Oct 12 23:16:32 2013 +0200
+++ b/Lib/test/test_fractions.py	Sat Oct 12 22:22:42 2013 +0100
@@ -12,6 +12,7 @@
 from pickle import dumps, loads
 F = fractions.Fraction
 gcd = fractions.gcd
+lcm = fractions.lcm
 
 class DummyFloat(object):
     """Dummy float class for testing comparisons with Fractions"""
@@ -94,6 +95,35 @@
         self.assertEqual(12, gcd(120, 84))
         self.assertEqual(-12, gcd(84, -120))
 
+class LcmTest(unittest.TestCase):
+    """The Least Common Multiple (LCM) of two integers (a,b) is the smallest
+    integer that both a and b divide into.
+
+    Note 1: LCM(a,b) * GCD(a,b) = a * b
+
+    Note 2: GCD(a,b) is often written as HCF(a,b) (Highest Common Factor)
+    """
+    
+    def test_lcm_int(self):
+        """ lcm should return an int, not a float """
+        self.assertTrue(isinstance(lcm(1, 2), int))
+    
+    def test_lcm(self):
+        """ test the basic cases, swapping arguments as lcm is symmetric."""
+        for answer,a,b in [(1,1,1),
+                (2,1,2),
+                (6,2,3),
+                (4,2,4),
+                (30,5,6),
+                (30,10,15)]:
+            self.assertEqual(answer,lcm(a,b))
+            self.assertEqual(answer,lcm(b,a))
+
+    def test_lcm_with_gcd(self):
+        """ lcm(a,b) * gcd(a,b) = a*b which allows an automatic co-test """
+        for a in range(1,20):
+            for b in range(1,20):
+                self.assertEqual(a*b, lcm(a, b) * gcd(a, b))
 
 def _components(r):
     return (r.numerator, r.denominator)
@@ -606,7 +636,7 @@
         self.assertRaises(AttributeError, setattr, r, 'a', 10)
 
 def test_main():
-    run_unittest(FractionTest, GcdTest)
+    run_unittest(FractionTest, GcdTest,LcmTest)
 
 if __name__ == '__main__':
     test_main()