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copied!<p>Below is a simple implementation of module <code>spam</code> with one function <code>myiter(int)</code> returning iterator:</p> <pre><code>import spam for i in spam.myiter(10): print i </code></pre> <p>prints numbers from 0 to 9.</p> <p>It is simpler then your case but shows main points: defining object with standard <code>__iter__()</code> and <code>next()</code> methods, and implementing iterator behaviour including raising <code>StopIteration</code> when appropriate.</p> <p>In your case iterator object needs to hold reference to Sequence (so you'll need deallocator method for it to Py_DECREF it). The sequence itself needs to implement <code>__iter()__</code> and create an iterator inside it.</p> <hr> <p>Structure containing state of iterator. (In your version instead of m, it would have reference to Sequence.)</p> <pre><code>typedef struct { PyObject_HEAD long int m; long int i; } spam_MyIter; </code></pre> <p>Iterator's <code>__iter__()</code> method. It always simply returns <code>self</code>. It allows for both iterator and collection to be treated the same in constructs like <code>for ... in ...</code>.</p> <pre><code>PyObject* spam_MyIter_iter(PyObject *self) { Py_INCREF(self); return self; } </code></pre> <p>Implementation of our iteration: <code>next()</code> method.</p> <pre><code>PyObject* spam_MyIter_iternext(PyObject *self) { spam_MyIter *p = (spam_MyIter *)self; if (p->i < p->m) { PyObject *tmp = Py_BuildValue("l", p->i); (p->i)++; return tmp; } else { /* Raising of standard StopIteration exception with empty value. */ PyErr_SetNone(PyExc_StopIteration); return NULL; } } </code></pre> <p>We need extended version of <code>PyTypeObject</code> structure to provide Python with information about <code>__iter__()</code> and <code>next()</code>. We want them to be called efficiently, so no name-based lookup in dictionary.</p> <pre><code>static PyTypeObject spam_MyIterType = { PyObject_HEAD_INIT(NULL) 0, /*ob_size*/ "spam._MyIter", /*tp_name*/ sizeof(spam_MyIter), /*tp_basicsize*/ 0, /*tp_itemsize*/ 0, /*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*/ 0, /*tp_getattro*/ 0, /*tp_setattro*/ 0, /*tp_as_buffer*/ Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_ITER, /* tp_flags: Py_TPFLAGS_HAVE_ITER tells python to use tp_iter and tp_iternext fields. */ "Internal myiter iterator object.", /* tp_doc */ 0, /* tp_traverse */ 0, /* tp_clear */ 0, /* tp_richcompare */ 0, /* tp_weaklistoffset */ spam_MyIter_iter, /* tp_iter: __iter__() method */ spam_MyIter_iternext /* tp_iternext: next() method */ }; </code></pre> <p><code>myiter(int)</code> function creates iterator.</p> <pre><code>static PyObject * spam_myiter(PyObject *self, PyObject *args) { long int m; spam_MyIter *p; if (!PyArg_ParseTuple(args, "l", &m)) return NULL; /* I don't need python callable __init__() method for this iterator, so I'll simply allocate it as PyObject and initialize it by hand. */ p = PyObject_New(spam_MyIter, &spam_MyIterType); if (!p) return NULL; /* I'm not sure if it's strictly necessary. */ if (!PyObject_Init((PyObject *)p, &spam_MyIterType)) { Py_DECREF(p); return NULL; } p->m = m; p->i = 0; return (PyObject *)p; } </code></pre> <p>The rest is pretty boring...</p> <pre><code>static PyMethodDef SpamMethods[] = { {"myiter", spam_myiter, METH_VARARGS, "Iterate from i=0 while i<m."}, {NULL, NULL, 0, NULL} /* Sentinel */ }; PyMODINIT_FUNC initspam(void) { PyObject* m; spam_MyIterType.tp_new = PyType_GenericNew; if (PyType_Ready(&spam_MyIterType) < 0) return; m = Py_InitModule("spam", SpamMethods); Py_INCREF(&spam_MyIterType); PyModule_AddObject(m, "_MyIter", (PyObject *)&spam_MyIterType); } </code></pre>

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