- New builtin function enumerate(x), from PEP 279. Example:

  enumerate("abc") is an iterator returning (0,"a"), (1,"b"), (2,"c").
  The argument can be an arbitrary iterable object.

Include/Python.h

@@ -91,6 +91,7 @@
 #include "tupleobject.h"
 #include "listobject.h"
 #include "dictobject.h"
+#include "enumobject.h"
 #include "methodobject.h"
 #include "moduleobject.h"
 #include "funcobject.h"

Include/enumobject.h

+#ifndef Py_ENUMOBJECT_H
+#define Py_ENUMOBJECT_H
+
+/* Enumerate Object */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern DL_IMPORT(PyTypeObject) PyEnum_Type;
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* !Py_ENUMOBJECT_H */

Lib/test/test_enumerate.py

+from __future__ import generators
+import unittest
+
+import test_support
+
+seq, res = 'abc', [(0,'a'), (1,'b'), (2,'c')]
+
+class G:
+    'Sequence using __getitem__'
+    def __init__(self, seqn):
+        self.seqn = seqn
+    def __getitem__(self, i):
+        return self.seqn[i]
+
+class I:
+    'Sequence using iterator protocol'
+    def __init__(self, seqn):
+        self.seqn = seqn
+        self.i = 0
+    def __iter__(self):
+        return self
+    def next(self):
+        if self.i >= len(self.seqn): raise StopIteration
+        v = self.seqn[self.i]
+        self.i += 1
+        return v
+
+class Ig:
+    'Sequence using iterator protocol defined with a generator'
+    def __init__(self, seqn):
+        self.seqn = seqn
+        self.i = 0
+    def __iter__(self):
+        for val in self.seqn:
+            yield val
+
+class X:
+    'Missing __getitem__ and __iter__'
+    def __init__(self, seqn):
+        self.seqn = seqn
+        self.i = 0
+    def next(self):
+        if self.i >= len(self.seqn): raise StopIteration
+        v = self.seqn[self.i]
+        self.i += 1
+        return v
+
+class E:
+    'Test propagation of exceptions'
+    def __init__(self, seqn):
+        self.seqn = seqn
+        self.i = 0
+    def __iter__(self):
+        return self
+    def next(self):
+        3/0
+
+class N:
+    'Iterator missing next()'
+    def __init__(self, seqn):
+        self.seqn = seqn
+        self.i = 0
+    def __iter__(self):
+        return self
+
+class EnumerateTestCase(unittest.TestCase):
+
+    enum = enumerate
+
+    def test_basicfunction(self):
+        self.assertEqual(type(self.enum(seq)), self.enum)
+        e = self.enum(seq)
+        self.assertEqual(iter(e), e)
+        self.assertEqual(list(self.enum(seq)), res)
+        self.enum.__doc__
+
+    def test_getitemseqn(self):
+        self.assertEqual(list(self.enum(G(seq))), res)
+        e = self.enum(G(''))
+        self.assertRaises(StopIteration, e.next)
+
+    def test_iteratorseqn(self):
+        self.assertEqual(list(self.enum(I(seq))), res)
+        e = self.enum(I(''))
+        self.assertRaises(StopIteration, e.next)
+
+    def test_iteratorgenerator(self):
+        self.assertEqual(list(self.enum(Ig(seq))), res)
+        e = self.enum(Ig(''))
+        self.assertRaises(StopIteration, e.next)
+
+    def test_noniterable(self):
+        self.assertRaises(TypeError, self.enum, X(seq))
+
+    def test_illformediterable(self):
+        self.assertRaises(TypeError, list, self.enum(N(seq)))
+
+    def test_exception_propagation(self):
+        self.assertRaises(ZeroDivisionError, list, self.enum(E(seq)))
+
+class MyEnum(enumerate):
+    pass
+
+class SubclassTestCase(EnumerateTestCase):
+
+    enum = MyEnum
+
+def suite():
+    suite = unittest.TestSuite()
+    suite.addTest(unittest.makeSuite(EnumerateTestCase))
+    suite.addTest(unittest.makeSuite(SubclassTestCase))
+    return suite
+
+def test_main():
+    test_support.run_suite(suite())
+
+if __name__ == "__main__":
+    test_main()

Makefile.pre.in

@@ -257,6 +257,7 @@ OBJECT_OBJS=	\
 		Objects/cobject.o \
 		Objects/complexobject.o \
 		Objects/descrobject.o \
+		Objects/enumobject.o \
 		Objects/fileobject.o \
 		Objects/floatobject.o \
 		Objects/frameobject.o \
@@ -443,6 +444,7 @@ PYTHON_HEADERS= \
 		Include/complexobject.h \
 		Include/descrobject.h \
 		Include/dictobject.h \
+		Include/enumobject.h \
 		Include/fileobject.h \
 		Include/floatobject.h \
 		Include/funcobject.h \

Misc/NEWS

@@ -6,6 +6,10 @@ Type/class unification and new-style classes
 
 Core and builtins
 
+- New builtin function enumerate(x), from PEP 279.  Example:
+  enumerate("abc") is an iterator returning (0,"a"), (1,"b"), (2,"c").
+  The argument can be an arbitrary iterable object.
+
 - The assert statement no longer tests __debug__ at runtime.  This means
   that assert statements cannot be disabled by assigning a false value
   to __debug__.

Objects/enumobject.c

+/* enumerate object */
+
+#include "Python.h"
+
+typedef struct {
+	PyObject_HEAD
+	long      en_index;        /* current index of enumeration */
+	PyObject* en_sit;          /* secondary iterator of enumeration */
+} enumobject;
+
+PyTypeObject PyEnum_Type;
+
+static PyObject *
+enum_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
+{
+	enumobject *en;
+	PyObject *seq = NULL;
+	static char *kwlist[] = {"sequence", 0};
+
+	if (!PyArg_ParseTupleAndKeywords(args, kwds, "O:enumerate", kwlist,
+					 &seq))
+		return NULL;
+
+	en = (enumobject *)type->tp_alloc(type, 0);
+	if (en == NULL)
+		return NULL;
+	en->en_index = 0;
+	en->en_sit = PyObject_GetIter(seq);
+	if (en->en_sit == NULL) {
+		Py_DECREF(en);
+		return NULL;
+	}
+	return (PyObject *)en;
+}
+
+static void
+enum_dealloc(enumobject *en)
+{
+	PyObject_GC_UnTrack(en);
+	Py_XDECREF(en->en_sit);
+	en->ob_type->tp_free(en);
+}
+
+static int
+enum_traverse(enumobject *en, visitproc visit, void *arg)
+{
+	if (en->en_sit)
+		return visit(en->en_sit, arg);
+	return 0;
+}
+
+static PyObject *
+enum_next(enumobject *en)
+{
+	PyObject *result;
+	PyObject *next_index;
+
+	PyObject *next_item = PyIter_Next(en->en_sit);
+	if (next_item == NULL)
+		return NULL;
+
+	result = PyTuple_New(2);
+	if (result == NULL) {
+		Py_DECREF(next_item);
+		return NULL;
+	}
+
+	next_index = PyInt_FromLong(en->en_index++);
+	if (next_index == NULL) {
+		Py_DECREF(next_item);
+		Py_DECREF(result);
+		return NULL;
+	}
+
+	PyTuple_SET_ITEM(result, 0, next_index);
+	PyTuple_SET_ITEM(result, 1, next_item);
+	return result;
+}
+
+static PyObject *
+enum_getiter(PyObject *en)
+{
+	Py_INCREF(en);
+	return en;
+}
+
+static PyMethodDef enum_methods[] = {
+	{"next",    (PyCFunction)enum_next, METH_NOARGS,
+	 "return the next (index, value) pair, or raise StopIteration"},
+	{NULL,      NULL}       /* sentinel */
+};
+
+static char enum_doc[] =
+	"enumerate(iterable) -> create an enumerating-iterator";
+
+PyTypeObject PyEnum_Type = {
+	PyObject_HEAD_INIT(&PyType_Type)
+	0,                              /* ob_size */
+	"enumerate",                    /* tp_name */
+	sizeof(enumobject),             /* tp_basicsize */
+	0,                              /* tp_itemsize */
+	/* methods */
+	(destructor)enum_dealloc,       /* tp_dealloc */
+	0,                              /* tp_print */
+	0,                              /* tp_getattr */
+	0,                              /* tp_setattr */
+	0,                              /* tp_compare */
+	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 */
+	enum_doc,                       /* tp_doc */
+	(traverseproc)enum_traverse,    /* tp_traverse */
+	0,                              /* tp_clear */
+	0,                              /* tp_richcompare */
+	0,                              /* tp_weaklistoffset */
+	(getiterfunc)enum_getiter,      /* tp_iter */
+	(iternextfunc)enum_next,        /* tp_iternext */
+	enum_methods,                   /* 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 */
+	PyType_GenericAlloc,            /* tp_alloc */
+	enum_new,                       /* tp_new */
+	PyObject_GC_Del,                /* tp_free */
+};

Python/bltinmodule.c

@@ -1864,6 +1864,7 @@ _PyBuiltin_Init(void)
 	SETBUILTIN("complex",		&PyComplex_Type);
 #endif
 	SETBUILTIN("dict",		&PyDict_Type);
+ 	SETBUILTIN("enumerate",		&PyEnum_Type);	
 	SETBUILTIN("float",		&PyFloat_Type);
 	SETBUILTIN("property",		&PyProperty_Type);
 	SETBUILTIN("int",		&PyInt_Type);