Add itertools.accumulate().

Lib/test/test_itertools.py

@@ -56,6 +56,23 @@ def fact(n):
     return prod(range(1, n+1))
 
 class TestBasicOps(unittest.TestCase):
+
+    def test_accumulate(self):
+        self.assertEqual(list(accumulate(range(10))),               # one positional arg
+                         [0, 1, 3, 6, 10, 15, 21, 28, 36, 45])
+        self.assertEqual(list(accumulate(range(10), 100)),          # two positional args
+            [100, 101, 103, 106, 110, 115, 121, 128, 136, 145])
+        self.assertEqual(list(accumulate(iterable=range(10), start=100)),   # kw args
+            [100, 101, 103, 106, 110, 115, 121, 128, 136, 145])
+        for typ in int, complex, Decimal, Fraction:                 # multiple types
+            self.assertEqual(list(accumulate(range(10), typ(0))),
+                list(map(typ, [0, 1, 3, 6, 10, 15, 21, 28, 36, 45])))
+        self.assertEqual(list(accumulate([])), [])                  # empty iterable
+        self.assertRaises(TypeError, accumulate, range(10), 0, 5)   # too many args
+        self.assertRaises(TypeError, accumulate)                    # too few args
+        self.assertRaises(TypeError, accumulate, range(10), x=7)    # unexpected kwd args
+        self.assertRaises(TypeError, list, accumulate([1, []]))     # args that don't add
+
     def test_chain(self):
 
         def chain2(*iterables):
@@ -932,6 +949,9 @@ class TestBasicOps(unittest.TestCase):
 
 class TestExamples(unittest.TestCase):
 
+    def test_accumlate(self):
+        self.assertEqual(list(accumulate([1,2,3,4,5])), [1, 3, 6, 10, 15])
+
     def test_chain(self):
         self.assertEqual(''.join(chain('ABC', 'DEF')), 'ABCDEF')
 
@@ -1019,6 +1039,10 @@ class TestGC(unittest.TestCase):
         next(iterator)
         del container, iterator
 
+    def test_accumulate(self):
+        a = []
+        self.makecycle(accumulate([1,2,a,3]), a)
+
     def test_chain(self):
         a = []
         self.makecycle(chain(a), a)
@@ -1188,6 +1212,17 @@ def L(seqn):
 
 class TestVariousIteratorArgs(unittest.TestCase):
 
+    def test_accumulate(self):
+        s = [1,2,3,4,5]
+        r = [1,3,6,10,15]
+        n = len(s)
+        for g in (G, I, Ig, L, R):
+            self.assertEqual(list(accumulate(g(s))), r)
+        self.assertEqual(list(accumulate(S(s))), [])
+        self.assertRaises(TypeError, accumulate, X(s))
+        self.assertRaises(TypeError, accumulate, N(s))
+        self.assertRaises(ZeroDivisionError, list, accumulate(E(s)))
+
     def test_chain(self):
         for s in ("123", "", range(1000), ('do', 1.2), range(2000,2200,5)):
             for g in (G, I, Ig, S, L, R):