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):

Misc/NEWS

@@ -46,6 +46,8 @@ Core and Builtins
 Library
 -------
 
+- Added itertools.accumulate().
+
 - Issue #4113: Added custom ``__repr__`` method to ``functools.partial``.
   Original patch by Daniel Urban.
 

Modules/itertoolsmodule.c

@@ -2584,6 +2584,146 @@ static PyTypeObject permutations_type = {
     PyObject_GC_Del,                    /* tp_free */
 };
 
+/* accumulate object ************************************************************/
+
+typedef struct {
+    PyObject_HEAD
+    PyObject *total;
+    PyObject *it;
+} accumulateobject;
+
+static PyTypeObject accumulate_type;
+
+static PyObject *
+accumulate_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
+{
+    static char *kwargs[] = {"iterable", "start", NULL};
+    PyObject *iterable;
+    PyObject *it;
+    PyObject *start = NULL;
+    accumulateobject *lz;
+
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|O:accumulate",
+				                     kwargs, &iterable, &start))
+	return NULL;
+
+    /* Get iterator. */
+    it = PyObject_GetIter(iterable);
+    if (it == NULL)
+        return NULL;
+
+    /* Default start value */
+    if (start == NULL) {
+	    start = PyLong_FromLong(0);
+	    if (start == NULL) {
+	        Py_DECREF(it);
+	        return NULL;
+	    }
+    } else {
+        Py_INCREF(start);
+    }
+
+    /* create accumulateobject structure */
+    lz = (accumulateobject *)type->tp_alloc(type, 0);
+    if (lz == NULL) {
+        Py_DECREF(it);
+	    Py_DECREF(start);
+            return NULL;
+    }
+
+    lz->total = start;
+    lz->it = it;
+    return (PyObject *)lz;
+}
+
+static void
+accumulate_dealloc(accumulateobject *lz)
+{
+    PyObject_GC_UnTrack(lz);
+    Py_XDECREF(lz->total);
+    Py_XDECREF(lz->it);
+    Py_TYPE(lz)->tp_free(lz);
+}
+
+static int
+accumulate_traverse(accumulateobject *lz, visitproc visit, void *arg)
+{
+    Py_VISIT(lz->it);
+    Py_VISIT(lz->total);
+    return 0;
+}
+
+static PyObject *
+accumulate_next(accumulateobject *lz)
+{
+    PyObject *val, *oldtotal, *newtotal;
+    
+    val = PyIter_Next(lz->it);
+    if (val == NULL)
+        return NULL;
+    
+    newtotal = PyNumber_Add(lz->total, val);
+	Py_DECREF(val);
+    if (newtotal == NULL)
+	    return NULL;
+
+    oldtotal = lz->total;
+    lz->total = newtotal;
+    Py_DECREF(oldtotal);
+    
+    Py_INCREF(newtotal);
+    return newtotal;
+}
+
+PyDoc_STRVAR(accumulate_doc,
+"accumulate(iterable, start=0) --> accumulate object\n\
+\n\
+Return series of accumulated sums.");
+
+static PyTypeObject accumulate_type = {
+    PyVarObject_HEAD_INIT(NULL, 0)
+    "itertools.accumulate",             /* tp_name */
+    sizeof(accumulateobject),           /* tp_basicsize */
+    0,                                  /* tp_itemsize */
+    /* methods */
+    (destructor)accumulate_dealloc,     /* tp_dealloc */
+    0,                                  /* tp_print */
+    0,                                  /* tp_getattr */
+    0,                                  /* tp_setattr */
+    0,                                  /* tp_reserved */
+    0,                                  /* tp_repr */
+    0,                                  /* tp_as_number */
+    0,                                  /* tp_as_sequence */
+    0,                                  /* tp_as_mapping */
+    0,                                  /* tp_hash */
+    0,                                  /* tp_call */
+    0,                                  /* tp_str */
+    PyObject_GenericGetAttr,            /* tp_getattro */
+    0,                                  /* tp_setattro */
+    0,                                  /* tp_as_buffer */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
+        Py_TPFLAGS_BASETYPE,            /* tp_flags */
+    accumulate_doc,                     /* tp_doc */
+    (traverseproc)accumulate_traverse,  /* tp_traverse */
+    0,                                  /* tp_clear */
+    0,                                  /* tp_richcompare */
+    0,                                  /* tp_weaklistoffset */
+    PyObject_SelfIter,                  /* tp_iter */
+    (iternextfunc)accumulate_next,      /* tp_iternext */
+    0,                                  /* tp_methods */
+    0,                                  /* tp_members */
+    0,                                  /* tp_getset */
+    0,                                  /* tp_base */
+    0,                                  /* tp_dict */
+    0,                                  /* tp_descr_get */
+    0,                                  /* tp_descr_set */
+    0,                                  /* tp_dictoffset */
+    0,                                  /* tp_init */
+    0,                                  /* tp_alloc */
+    accumulate_new,                     /* tp_new */
+    PyObject_GC_Del,                    /* tp_free */
+};
+
 
 /* compress object ************************************************************/
 
@@ -3496,6 +3636,7 @@ cycle(p) --> p0, p1, ... plast, p0, p1, ...\n\
 repeat(elem [,n]) --> elem, elem, elem, ... endlessly or up to n times\n\
 \n\
 Iterators terminating on the shortest input sequence:\n\
+accumulate(p, start=0) --> p0, p0+p1, p0+p1+p2\n\
 chain(p, q, ...) --> p0, p1, ... plast, q0, q1, ... \n\
 compress(data, selectors) --> (d[0] if s[0]), (d[1] if s[1]), ...\n\
 dropwhile(pred, seq) --> seq[n], seq[n+1], starting when pred fails\n\
@@ -3541,6 +3682,7 @@ PyInit_itertools(void)
     PyObject *m;
     char *name;
     PyTypeObject *typelist[] = {
+        &accumulate_type,
         &combinations_type,
         &cwr_type,
         &cycle_type,