Question

我正在编写我对Python的第一个C扩展，并且对我的引用计数感到困惑。这就是我想要做的。

我在for循环中填充了一个dict：

mydict = PyDict_New();

for (...)
{
    pair = PyTuple_Pack(2, PyString_FromString("some string"),
          PyString_FromString("some other string"));

    /* at this point, the refcnt for the tuple is 1, the refcnts for the
       2 string items are 2. Because according to the source, PyString_FromString
       does an INCREF, and PyTuple_Pack() does an INCREF on its items
     */

    PyDict_SetItem(mydict, PyString_FromString("some key"), pair);

    /* At this point, the key's refcnt is 2.  PyString_FromString sets it to 1 and 
       PyDict_SetItem INCREF's it. Ditto for pair since PyDict_SetItem also INCREF's
       the value.
     */

    Py_DECREF(pair);

    /* pair's refcnt is 1 which makes sense to me since mydict now owns the tuple, 
       but the refcnt for its items are still at 2.  I don't understand this part.
     */
}

return mydict;

我的引用是否正确？在C API文档中，它特别建议使用PyObject_FromXXX 作为PyTuple_SetItem或PyList_SetItem的参数起作用，因为它们“窃取”了引用。

没有记录PyDict_SetItem是否窃取引用。我猜它不是在哪种情况下，我应该做

first = PyString_FromString("some string");
second = PyString_FromString("some other string");
pair = PyTuple_Pack(2, first, second);
Py_DECREF(second);
Py_DECREF(first);

我是对的吗？

Answer 1

如果你看一下PyTuple_Pack的CPython源代码（Objects / tupleobject.c），你会发现它确实增加了每个打包对象的引用计数。如果您改为执行PyTuple_New后跟PyTuple_SetItem调用，则不需要减少引用计数，因为SetItem会窃取引用。

最后，您可能只想使用Py_BuildValue（“（ss）”，“some string”，“some other string”）; 它将为您构建您的元组，它将为您创建PyStrings： http://docs.python.org/c-api/arg.html#Py_BuildValue

引用计数在Python C扩展中

1 个答案: