Copy reduce() to _functools so to have functools.reduce() not raise a warning

from usage under -3.

Lib/functools.py

@@ -7,8 +7,7 @@
 #   Copyright (C) 2006 Python Software Foundation.
 # See C source code for _functools credits/copyright
 
-from _functools import partial
-from __builtin__ import reduce
+from _functools import partial, reduce
 
 # update_wrapper() and wraps() are tools to help write
 # wrapper functions that can handle naive introspection

Lib/test/test_functools.py

@@ -267,6 +267,48 @@ class TestWraps(TestUpdateWrapper):
         self.assertEqual(wrapper.dict_attr, f.dict_attr)
 
 
+class TestReduce(unittest.TestCase):
+
+    def test_reduce(self):
+        class Squares:
+
+            def __init__(self, max):
+                self.max = max
+                self.sofar = []
+
+            def __len__(self): return len(self.sofar)
+
+            def __getitem__(self, i):
+                if not 0 <= i < self.max: raise IndexError
+                n = len(self.sofar)
+                while n <= i:
+                    self.sofar.append(n*n)
+                    n += 1
+                return self.sofar[i]
+
+        reduce = functools.reduce
+        self.assertEqual(reduce(lambda x, y: x+y, ['a', 'b', 'c'], ''), 'abc')
+        self.assertEqual(
+            reduce(lambda x, y: x+y, [['a', 'c'], [], ['d', 'w']], []),
+            ['a','c','d','w']
+        )
+        self.assertEqual(reduce(lambda x, y: x*y, range(2,8), 1), 5040)
+        self.assertEqual(
+            reduce(lambda x, y: x*y, range(2,21), 1L),
+            2432902008176640000L
+        )
+        self.assertEqual(reduce(lambda x, y: x+y, Squares(10)), 285)
+        self.assertEqual(reduce(lambda x, y: x+y, Squares(10), 0), 285)
+        self.assertEqual(reduce(lambda x, y: x+y, Squares(0), 0), 0)
+        self.assertRaises(TypeError, reduce)
+        self.assertRaises(TypeError, reduce, 42, 42)
+        self.assertRaises(TypeError, reduce, 42, 42, 42)
+        self.assertEqual(reduce(42, "1"), "1") # func is never called with one item
+        self.assertEqual(reduce(42, "", "1"), "1") # func is never called with one item
+        self.assertRaises(TypeError, reduce, 42, (42, 42))
+
+
+
 
 def test_main(verbose=None):
     import sys
@@ -275,7 +317,8 @@ def test_main(verbose=None):
         TestPartialSubclass,
         TestPythonPartial,
         TestUpdateWrapper,
-        TestWraps
+        TestWraps,
+        TestReduce,
     )
     test_support.run_unittest(*test_classes)
 

Misc/NEWS

@@ -41,6 +41,9 @@ Core and Builtins
 Library
 -------
 
+- Copied the implementation of reduce() to _functools.reduce() to have a
+  version that did not raise a DeprecationWarning under -3.
+
 - Issue #3205: When iterating over a BZ2File fails allocating memory, raise
   a MemoryError rather than silently stop the iteration.
 

Modules/_functoolsmodule.c

@@ -9,6 +9,84 @@
    All rights reserved.
 */
 
+/* reduce() *************************************************************/
+
+static PyObject *
+functools_reduce(PyObject *self, PyObject *args)
+{
+	PyObject *seq, *func, *result = NULL, *it;
+
+	if (!PyArg_UnpackTuple(args, "reduce", 2, 3, &func, &seq, &result))
+		return NULL;
+	if (result != NULL)
+		Py_INCREF(result);
+
+	it = PyObject_GetIter(seq);
+	if (it == NULL) {
+		PyErr_SetString(PyExc_TypeError,
+		    "reduce() arg 2 must support iteration");
+		Py_XDECREF(result);
+		return NULL;
+	}
+
+	if ((args = PyTuple_New(2)) == NULL)
+		goto Fail;
+
+	for (;;) {
+		PyObject *op2;
+
+		if (args->ob_refcnt > 1) {
+			Py_DECREF(args);
+			if ((args = PyTuple_New(2)) == NULL)
+				goto Fail;
+		}
+
+		op2 = PyIter_Next(it);
+		if (op2 == NULL) {
+			if (PyErr_Occurred())
+				goto Fail;
+ 			break;
+		}
+
+		if (result == NULL)
+			result = op2;
+		else {
+			PyTuple_SetItem(args, 0, result);
+			PyTuple_SetItem(args, 1, op2);
+			if ((result = PyEval_CallObject(func, args)) == NULL)
+				goto Fail;
+		}
+	}
+
+	Py_DECREF(args);
+
+	if (result == NULL)
+		PyErr_SetString(PyExc_TypeError,
+			   "reduce() of empty sequence with no initial value");
+
+	Py_DECREF(it);
+	return result;
+
+Fail:
+	Py_XDECREF(args);
+	Py_XDECREF(result);
+	Py_DECREF(it);
+	return NULL;
+}
+
+PyDoc_STRVAR(reduce_doc,
+"reduce(function, sequence[, initial]) -> value\n\
+\n\
+Apply a function of two arguments cumulatively to the items of a sequence,\n\
+from left to right, so as to reduce the sequence to a single value.\n\
+For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates\n\
+((((1+2)+3)+4)+5).  If initial is present, it is placed before the items\n\
+of the sequence in the calculation, and serves as a default when the\n\
+sequence is empty.");
+
+
+
+
 /* partial object **********************************************************/
 
 typedef struct {
@@ -247,6 +325,7 @@ PyDoc_STRVAR(module_doc,
 "Tools that operate on functions.");
 
 static PyMethodDef module_methods[] = {
+ 	{"reduce",	functools_reduce,     METH_VARARGS, reduce_doc},
  	{NULL,		NULL}		/* sentinel */
 };