Python C扩展中的引用计数

问题描述：

我正在为Python编写我的第一个C扩展，并对引用计数感到困惑。这是我想要做的。Python C扩展中的引用计数

我填充字典的for循环：

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;

是我裁判计数是否正确？在C API文档中，它特别建议使用PyObject_FromXXX 函数作为PyTuple_SetItem或PyList_SetItem的参数，因为它们“窃取”引用。

没有记录PyDict_SetItem是否盗取了引用。我猜它不会在这种情况下，我应该做的

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

我说得对不对？

这个问题似乎涉及：http://*.com/questions/6977161/where-should-i-put-py-incref-和py-decref-on-this-block-in-python-c-extension – Daenyth 2011-12-16 00:38:44

答

如果您查看PyTuple_Pack的CPython源代码（Objects/tupleobject.c），您会发现它的确会增加每个打包对象的引用计数。如果您改为执行PyTuple_New，然后执行PyTuple_SetItem调用，您将不需要减少引用计数，因为SetItem会窃取引用。最后，你可能只想使用Py_BuildValue（“（ss）”，“some string”，“some other string”）; 它将建立自己的元组你，它会为你创建PyStrings： http://docs.python.org/c-api/arg.html#Py_BuildValue

Python C扩展中的引用计数

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