text: /* enumerate object */
  
  #include "Python.h"
  
  typedef struct {
  	PyObject_HEAD
  	Py_ssize_t en_index;	   /* current index of enumeration */
  	PyObject* en_sit;          /* secondary iterator of enumeration */
  	PyObject* en_result;	   /* result tuple  */
  	PyObject* en_longindex;	   /* index for sequences >= PY_SSIZE_T_MAX */
  } enumobject;
  
  static PyObject *
  enum_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
  {
  	enumobject *en;
  	PyObject *seq = NULL;
  	PyObject *start = NULL;
  	static char *kwlist[] = {"sequence", "start", 0};
  
  	if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|O:enumerate", kwlist,
  					 &seq, &start))
  		return NULL;
  
  	en = (enumobject *)type->tp_alloc(type, 0);
  	if (en == NULL)
  		return NULL;
  	if (start != NULL) {
  		start = PyNumber_Index(start);
  		if (start == NULL) {
  			Py_DECREF(en);
  			return NULL;
  		}
  		assert(PyInt_Check(start) || PyLong_Check(start));
  		en->en_index = PyInt_AsSsize_t(start);
  		if (en->en_index == -1 && PyErr_Occurred()) {
  			PyErr_Clear();
  			en->en_index = PY_SSIZE_T_MAX;
  			en->en_longindex = start;
  		} else {
  			en->en_longindex = NULL;
  			Py_DECREF(start);
  		}
  	} else {
  		en->en_index = 0;
  		en->en_longindex = NULL;
  	}
  	en->en_sit = PyObject_GetIter(seq);
  	if (en->en_sit == NULL) {
  		Py_DECREF(en);
  		return NULL;
  	}
  	en->en_result = PyTuple_Pack(2, Py_None, Py_None);
  	if (en->en_result == NULL) {
  		Py_DECREF(en);
  		return NULL;
  	}
  	return (PyObject *)en;
  }
  
  static void
  enum_dealloc(enumobject *en)
  {
  	PyObject_GC_UnTrack(en);
  	Py_XDECREF(en->en_sit);
  	Py_XDECREF(en->en_result);
  	Py_XDECREF(en->en_longindex);
  	Py_TYPE(en)->tp_free(en);
  }
  
  static int
  enum_traverse(enumobject *en, visitproc visit, void *arg)
  {
  	Py_VISIT(en->en_sit);
  	Py_VISIT(en->en_result);
  	Py_VISIT(en->en_longindex);
  	return 0;
  }
  
  static PyObject *
  enum_next_long(enumobject *en, PyObject* next_item)
  {
  	static PyObject *one = NULL;
  	PyObject *result = en->en_result;
  	PyObject *next_index;
  	PyObject *stepped_up;
  
  	if (en->en_longindex == NULL) {
  		en->en_longindex = PyInt_FromSsize_t(PY_SSIZE_T_MAX);
  		if (en->en_longindex == NULL)
  			return NULL;
  	}
  	if (one == NULL) {
  		one = PyInt_FromLong(1);
  		if (one == NULL)
  			return NULL;
  	}
  	next_index = en->en_longindex;
  	assert(next_index != NULL);
  	stepped_up = PyNumber_Add(next_index, one);
  	if (stepped_up == NULL)
  		return NULL;
  	en->en_longindex = stepped_up;
  
  	if (result->ob_refcnt == 1) {
  		Py_INCREF(result);
  		Py_DECREF(PyTuple_GET_ITEM(result, 0));
  		Py_DECREF(PyTuple_GET_ITEM(result, 1));
  	} else {
  		result = PyTuple_New(2);
  		if (result == NULL) {
  			Py_DECREF(next_index);
  			Py_DECREF(next_item);
  			return NULL;
  		}
  	}
  	PyTuple_SET_ITEM(result, 0, next_index);
  	PyTuple_SET_ITEM(result, 1, next_item);
  	return result;
  }
  
  static PyObject *
  enum_next(enumobject *en)
  {
  	PyObject *next_index;
  	PyObject *next_item;
  	PyObject *result = en->en_result;
  	PyObject *it = en->en_sit;
  
  	next_item = (*Py_TYPE(it)->tp_iternext)(it);
  	if (next_item == NULL)
  		return NULL;
  
  	if (en->en_index == PY_SSIZE_T_MAX)
  		return enum_next_long(en, next_item);
  
  	next_index = PyInt_FromSsize_t(en->en_index);
  	if (next_index == NULL) {
  		Py_DECREF(next_item);
  		return NULL;
  	}
  	en->en_index++;
  
  	if (result->ob_refcnt == 1) {
  		Py_INCREF(result);
  		Py_DECREF(PyTuple_GET_ITEM(result, 0));
  		Py_DECREF(PyTuple_GET_ITEM(result, 1));
  	} else {
  		result = PyTuple_New(2);
  		if (result == NULL) {
  			Py_DECREF(next_index);
  			Py_DECREF(next_item);
  			return NULL;
  		}
  	}
  	PyTuple_SET_ITEM(result, 0, next_index);
  	PyTuple_SET_ITEM(result, 1, next_item);
  	return result;
  }
  
  PyDoc_STRVAR(enum_doc,
  "enumerate(iterable) -> iterator for index, value of iterable\n"
  "\n"
  "Return an enumerate object.  iterable must be another object that supports\n"
  "iteration.  The enumerate object yields pairs containing a count (from\n"
  "zero) and a value yielded by the iterable argument.  enumerate is useful\n"
  "for obtaining an indexed list: (0, seq[0]), (1, seq[1]), (2, seq[2]), ...");
  
  PyTypeObject PyEnum_Type = {
  	PyVarObject_HEAD_INIT(&PyType_Type, 0)
  	"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 */
  	PyObject_SelfIter,		/* tp_iter */
  	(iternextfunc)enum_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 */
  	PyType_GenericAlloc,            /* tp_alloc */
  	enum_new,                       /* tp_new */
  	PyObject_GC_Del,                /* tp_free */
  };
  
  /* Reversed Object ***************************************************************/
  
  typedef struct {
  	PyObject_HEAD
  	Py_ssize_t      index;
  	PyObject* seq;
  } reversedobject;
  
  static PyObject *
  reversed_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
  {
  	Py_ssize_t n;
  	PyObject *seq;
  	reversedobject *ro;
  
  	if (type == &PyReversed_Type && !_PyArg_NoKeywords("reversed()", kwds))
  		return NULL;
  
  	if (!PyArg_UnpackTuple(args, "reversed", 1, 1, &seq) )
  		return NULL;
  
  	if (PyObject_HasAttrString(seq, "__reversed__"))
  		return PyObject_CallMethod(seq, "__reversed__", NULL);
  
  	if (!PySequence_Check(seq)) {
  		PyErr_SetString(PyExc_TypeError,
  				"argument to reversed() must be a sequence");
  		return NULL;
  	}
  
  	n = PySequence_Size(seq);
  	if (n == -1)
  		return NULL;
  
  	ro = (reversedobject *)type->tp_alloc(type, 0);
  	if (ro == NULL)
  		return NULL;
  
  	ro->index = n-1;
  	Py_INCREF(seq);
  	ro->seq = seq;
  	return (PyObject *)ro;
  }
  
  static void
  reversed_dealloc(reversedobject *ro)
  {
  	PyObject_GC_UnTrack(ro);
  	Py_XDECREF(ro->seq);
  	Py_TYPE(ro)->tp_free(ro);
  }
  
  static int
  reversed_traverse(reversedobject *ro, visitproc visit, void *arg)
  {
  	Py_VISIT(ro->seq);
  	return 0;
  }
  
  static PyObject *
  reversed_next(reversedobject *ro)
  {
  	PyObject *item;
  	Py_ssize_t index = ro->index;
  
  	if (index >= 0) {
  		item = PySequence_GetItem(ro->seq, index);
  		if (item != NULL) {
  			ro->index--;
  			return item;
  		}
  		if (PyErr_ExceptionMatches(PyExc_IndexError) ||
  		    PyErr_ExceptionMatches(PyExc_StopIteration))
  			PyErr_Clear();
  	}
  	ro->index = -1;
  	Py_CLEAR(ro->seq);
  	return NULL;
  }
  
  PyDoc_STRVAR(reversed_doc,
  "reversed(sequence) -> reverse iterator over values of the sequence\n"
  "\n"
  "Return a reverse iterator");
  
  static PyObject *
  reversed_len(reversedobject *ro)
  {
  	Py_ssize_t position, seqsize;
  
  	if (ro->seq == NULL)
  		return PyInt_FromLong(0);
  	seqsize = PySequence_Size(ro->seq);
  	if (seqsize == -1)
  		return NULL;
  	position = ro->index + 1;
  	return PyInt_FromSsize_t((seqsize < position)  ?  0  :  position);
  }
  
  PyDoc_STRVAR(length_hint_doc, "Private method returning an estimate of len(list(it)).");
  
  static PyMethodDef reversediter_methods[] = {
  	{"__length_hint__", (PyCFunction)reversed_len, METH_NOARGS, length_hint_doc},
   	{NULL,		NULL}		/* sentinel */
  };
  
  PyTypeObject PyReversed_Type = {
  	PyVarObject_HEAD_INIT(&PyType_Type, 0)
  	"reversed",                     /* tp_name */
  	sizeof(reversedobject),         /* tp_basicsize */
  	0,                              /* tp_itemsize */
  	/* methods */
  	(destructor)reversed_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 */
  	reversed_doc,                   /* tp_doc */
  	(traverseproc)reversed_traverse,/* tp_traverse */
  	0,                              /* tp_clear */
  	0,                              /* tp_richcompare */
  	0,                              /* tp_weaklistoffset */
  	PyObject_SelfIter,		/* tp_iter */
  	(iternextfunc)reversed_next,    /* tp_iternext */
  	reversediter_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 */
  	reversed_new,                   /* tp_new */
  	PyObject_GC_Del,                /* tp_free */
  };
  