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<p>如何使用Python C API复制以下Python代码?</p>
<pre><code>class Sequence():
def __init__(self, max):
self.max = max
def data(self):
i = 0
while i < self.max:
yield i
i += 1
</code></pre>
<p>到目前为止,我有这个:</p>
<pre><code>#include <Python/Python.h>
#include <Python/structmember.h>
/* Define a new object class, Sequence. */
typedef struct {
PyObject_HEAD
size_t max;
} SequenceObject;
/* Instance variables */
static PyMemberDef Sequence_members[] = {
{"max", T_UINT, offsetof(SequenceObject, max), 0, NULL},
{NULL} /* Sentinel */
};
static int Sequence_Init(SequenceObject *self, PyObject *args, PyObject *kwds)
{
if (!PyArg_ParseTuple(args, "k", &(self->max))) {
return -1;
}
return 0;
}
static PyObject *Sequence_data(SequenceObject *self, PyObject *args);
/* Methods */
static PyMethodDef Sequence_methods[] = {
{"data", (PyCFunction)Sequence_data, METH_NOARGS,
"sequence.data() -> iterator object\n"
"Returns iterator of range [0, sequence.max)."},
{NULL} /* Sentinel */
};
/* Define new object type */
PyTypeObject Sequence_Type = {
PyObject_HEAD_INIT(NULL)
0, /* ob_size */
"Sequence", /* tp_name */
sizeof(SequenceObject), /* 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_BASETYPE, /* tp_flags*/
"Test generator object", /* tp_doc */
0, /* tp_traverse */
0, /* tp_clear */
0, /* tp_richcompare */
0, /* tp_weaklistoffset */
0, /* tp_iter */
0, /* tp_iternext */
0, /* tp_methods */
Sequence_members, /* tp_members */
0, /* tp_getset */
0, /* tp_base */
0, /* tp_dict */
0, /* tp_descr_get */
0, /* tp_descr_set */
0, /* tp_dictoffset */
(initproc)Sequence_init, /* tp_init */
0, /* tp_alloc */
PyType_GenericNew, /* tp_new */
};
static PyObject *Sequence_data(SequenceObject *self, PyObject *args)
{
/* Now what? */
}
</code></pre>
<p>但我不知道下一步该去哪里。有人能提些建议吗?</p>
<h2>编辑</h2>
<p>我想我遇到的主要问题是模拟<code>yield</code>语句。据我所知,它看起来很简单,但实际上很复杂,它创建了一个生成器,它有自己的<code>__iter__()</code>和<code>next()</code>方法,这些方法是自动调用的。搜索文档时,它似乎与<a href="http://docs.python.org/c-api/gen.html" rel="noreferrer">PyGenObject</a>关联;但是,如何创建此对象的新实例尚不清楚。<code>PyGen_New()</code>以a<code>PyFrameObject</code>作为参数,我能找到的唯一引用是<a href="http://docs.python.org/c-api/reflection.html" rel="noreferrer">^{<cd6>}</a>,这似乎不是我想要的(或者我错了?)。有没有人可以分享这方面的经验?</p>
<h2>进一步编辑</h2>
<p>当我(本质上)展开Python在幕后所做的工作时,我发现这一点更加清晰:</p>
<pre><code>class IterObject():
def __init__(self, max):
self.max = max
def __iter__(self):
self.i = 0
return self
def next(self):
if self.i >= self.max:
raise StopIteration
self.i += 1
return self.i
class Sequence():
def __init__(self, max):
self.max = max
def data(self):
return IterObject(self.max)
</code></pre>
<p>从技术上讲,顺序是一个一个的,但是你知道了。</p>
<p>唯一的问题是每次需要一个生成器时都创建一个新对象是非常烦人的——在Python中甚至比C中更烦人,因为定义一个新类型所需要的畸形。而且C中不能有<code>yield</code>语句,因为C没有闭包。我做了什么(因为我在Python API中找不到它-<em>请</em>给我指一个标准对象,如果它已经存在的话!)创建一个简单的泛型生成器对象类,该类为每个<code>next()</code>方法调用回调一个C函数。这里是(请注意,我还没有尝试编译,因为它还没有完成-请参阅下面的内容):</p>
<pre><code>#include <Python/Python.h>
#include <Python/structmember.h>
#include <stdlib.h>
/* A convenient, generic generator object. */
typedef PyObject *(*callback)(PyObject *callee, void *info) PyGeneratorCallback;
typedef struct {
PyObject HEAD
PyGeneratorCallback callback;
PyObject *callee;
void *callbackInfo; /* info to be passed along to callback function. */
bool freeInfo; /* true if |callbackInfo| should be free'()d when object
* dealloc's, false if not. */
} GeneratorObject;
static PyObject *Generator_iter(PyObject *self, PyObject *args)
{
Py_INCREF(self);
return self;
}
static PyObject *Generator_next(PyObject *self, PyObject *args)
{
return self->callback(self->callee, self->callbackInfo);
}
static PyMethodDef Generator_methods[] = {
{"__iter__", (PyCFunction)Generator_iter, METH_NOARGS, NULL},
{"next", (PyCFunction)Generator_next, METH_NOARGS, NULL},
{NULL} /* Sentinel */
};
static void Generator_dealloc(GenericEventObject *self)
{
if (self->freeInfo && self->callbackInfo != NULL) {
free(self->callbackInfo);
}
self->ob_type->tp_free((PyObject *)self);
}
PyTypeObject Generator_Type = {
PyObject_HEAD_INIT(NULL)
0, /* ob_size */
"Generator", /* tp_name */
sizeof(GeneratorObject), /* tp_basicsize */
0, /* tp_itemsize */
Generator_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 */
0, /* tp_getattro */
0, /* tp_setattro */
0, /* tp_as_buffer */
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /* tp_flags*/
0, /* tp_doc */
0, /* tp_traverse */
0, /* tp_clear */
0, /* tp_richcompare */
0, /* tp_weaklistoffset */
0, /* tp_iter */
0, /* 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 */
PyType_GenericNew, /* tp_new */
};
/* Returns a new generator object with the given callback function
* and arguments. */
PyObject *Generator_New(PyObject *callee, void *info,
bool freeInfo, PyGeneratorCallback callback)
{
GeneratorObject *generator = (GeneratorObject *)_PyObject_New(&Generator_Type);
if (generator == NULL) return NULL;
generator->callee = callee;
generator->info = info;
generator->callback = callback;
self->freeInfo = freeInfo;
return (PyObject *)generator;
}
/* End of Generator definition. */
/* Define a new object class, Sequence. */
typedef struct {
PyObject_HEAD
size_t max;
} SequenceObject;
/* Instance variables */
static PyMemberDef Sequence_members[] = {
{"max", T_UINT, offsetof(SequenceObject, max), 0, NULL},
{NULL} /* Sentinel */
}
static int Sequence_Init(SequenceObject *self, PyObject *args, PyObject *kwds)
{
if (!PyArg_ParseTuple(args, "k", &self->max)) {
return -1;
}
return 0;
}
static PyObject *Sequence_data(SequenceObject *self, PyObject *args);
/* Methods */
static PyMethodDef Sequence_methods[] = {
{"data", (PyCFunction)Sequence_data, METH_NOARGS,
"sequence.data() -> iterator object\n"
"Returns generator of range [0, sequence.max)."},
{NULL} /* Sentinel */
};
/* Define new object type */
PyTypeObject Sequence_Type = {
PyObject_HEAD_INIT(NULL)
0, /* ob_size */
"Sequence", /* tp_name */
sizeof(SequenceObject), /* 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_BASETYPE, /* tp_flags*/
"Test generator object", /* tp_doc */
0, /* tp_traverse */
0, /* tp_clear */
0, /* tp_richcompare */
0, /* tp_weaklistoffset */
0, /* tp_iter */
0, /* tp_iternext */
0, /* tp_methods */
Sequence_members, /* tp_members */
0, /* tp_getset */
0, /* tp_base */
0, /* tp_dict */
0, /* tp_descr_get */
0, /* tp_descr_set */
0, /* tp_dictoffset */
(initproc)Sequence_init, /* tp_init */
0, /* tp_alloc */
PyType_GenericNew, /* tp_new */
};
static PyObject *Sequence_data(SequenceObject *self, PyObject *args)
{
size_t *info = malloc(sizeof(size_t));
if (info == NULL) return NULL;
*info = 0;
/* |info| will be free'()d by the returned generator object. */
GeneratorObject *ret = Generator_New(self, info, true,
&Sequence_data_next_callback);
if (ret == NULL) {
free(info); /* Watch out for memory leaks! */
}
return ret;
}
PyObject *Sequence_data_next_callback(PyObject *self, void *info)
{
size_t i = info;
if (i > self->max) {
return NULL; /* TODO: How do I raise StopIteration here? I can't seem to find
* a standard exception. */
} else {
return Py_BuildValue("k", i++);
}
}
</code></pre>
<p>不过,不幸的是,我还没说完。我只剩下一个问题:如何用C API引发<code>StopIteration</code>异常?我好像在<a href="http://docs.python.org/c-api/exceptions.html#standard-exceptions" rel="noreferrer">Standard Exceptions</a>里找不到它。另外,也许更重要的是,这是解决这个问题的正确方法吗?</p>
<p>感谢所有关注此事的人。</p>