PyObject *
  _PyObject_GenericGetAttrWithDict(PyObject *obj, PyObject *name, PyObject *dict)
  {
  	// 获取obj的类型
  	PyTypeObject *tp = Py_TYPE(obj);
  	PyObject *descr = NULL;
  	PyObject *res = NULL;
  	descrgetfunc f;
  	Py_ssize_t dictoffset;
  	PyObject **dictptr;

  	if (!PyUnicode_Check(name)){
  		PyErr_Format(PyExc_TypeError,
  					 "attribute name must be string, not '%.200s'",
  					 name->ob_type->tp_name);
  		return NULL;
  	}
  	else
  		Py_INCREF(name);

  	if (tp->tp_dict == NULL) {
  		if (PyType_Ready(tp) < 0)
  			goto done;
  	}

  	// 获取类型中对应的属性descr
  	descr = _PyType_Lookup(tp, name);
  	Py_XINCREF(descr);

  	f = NULL;
  	if (descr != NULL) {
  		// 获取get descriptor并且判断是否为数据描述符
  		f = descr->ob_type->tp_descr_get;
  		if (f != NULL && PyDescr_IsData(descr)) {
  			res = f(descr, obj, (PyObject *)obj->ob_type);
  			goto done;
  		}
  	}

  	if (dict == NULL) {
  		/* Inline _PyObject_GetDictPtr */
  		dictoffset = tp->tp_dictoffset;
  		if (dictoffset != 0) {
  			if (dictoffset < 0) {
  				Py_ssize_t tsize;
  				size_t size;

  				tsize = ((PyVarObject *)obj)->ob_size;
  				if (tsize < 0)
  					tsize = -tsize;
  				size = _PyObject_VAR_SIZE(tp, tsize);

  				dictoffset += (long)size;
  				assert(dictoffset > 0);
  				assert(dictoffset % SIZEOF_VOID_P == 0);
  			}
  			dictptr = (PyObject **) ((char *)obj + dictoffset);
  			dict = *dictptr;
  		}
  	}
  	if (dict != NULL) {
  		Py_INCREF(dict);

  		// 在obj的__dict__中进行查找
  		res = PyDict_GetItem(dict, name);
  		if (res != NULL) {
  			Py_INCREF(res);
  			Py_DECREF(dict);
  			goto done;
  		}
  		Py_DECREF(dict);
  	}

  	if (f != NULL) {
  		// 通过非数据描述符的方式获取属性
  		res = f(descr, obj, (PyObject *)Py_TYPE(obj));
  		goto done;
  	}

  	if (descr != NULL) {
  		res = descr;
  		descr = NULL;
  		goto done;
  	}

  	PyErr_Format(PyExc_AttributeError,
  				 "'%.50s' object has no attribute '%U'",
  				 tp->tp_name, name);
    done:
  	Py_XDECREF(descr);
  	Py_DECREF(name);
  	return res;
  }

  int
  _PyObject_GenericSetAttrWithDict(PyObject *obj, PyObject *name,
  								 PyObject *value, PyObject *dict)
  {
  	// 获取obj的类型
  	PyTypeObject *tp = Py_TYPE(obj);
  	PyObject *descr;
  	descrsetfunc f;
  	PyObject **dictptr;
  	int res = -1;

  	if (!PyUnicode_Check(name)){
  		PyErr_Format(PyExc_TypeError,
  					 "attribute name must be string, not '%.200s'",
  					 name->ob_type->tp_name);
  		return -1;
  	}

  	if (tp->tp_dict == NULL && PyType_Ready(tp) < 0)
  		return -1;

  	Py_INCREF(name);

      // 查找类型中对应的属性
  	descr = _PyType_Lookup(tp, name);
  	Py_XINCREF(descr);

  	f = NULL;
  	if (descr != NULL) {

          // 获取set descriptor判断是否为数据描述符并且写属性
  		f = descr->ob_type->tp_descr_set;
  		if (f != NULL && PyDescr_IsData(descr)) {
  			res = f(descr, obj, value);
  			goto done;
  		}
  	}

  	if (dict == NULL) {
  		dictptr = _PyObject_GetDictPtr(obj);
  		if (dictptr != NULL) {
  			res = _PyObjectDict_SetItem(Py_TYPE(obj), dictptr, name, value);
  			if (res < 0 && PyErr_ExceptionMatches(PyExc_KeyError))
  				PyErr_SetObject(PyExc_AttributeError, name);
  			goto done;
  		}
  	}
  	if (dict != NULL) {
  		Py_INCREF(dict);

          // 通过obj的__dict__进行属性操作
  		if (value == NULL)
  			res = PyDict_DelItem(dict, name);
  		else
  			res = PyDict_SetItem(dict, name, value);
  		Py_DECREF(dict);
  		if (res < 0 && PyErr_ExceptionMatches(PyExc_KeyError))
  			PyErr_SetObject(PyExc_AttributeError, name);
  		goto done;
  	}

  	if (f != NULL) {

          // 以非数据描述符方式写属性
  		res = f(descr, obj, value);
  		goto done;
  	}

  	if (descr == NULL) {
  		PyErr_Format(PyExc_AttributeError,
  					 "'%.100s' object has no attribute '%U'",
  					 tp->tp_name, name);
  		goto done;
  	}

  	PyErr_Format(PyExc_AttributeError,
  				 "'%.50s' object attribute '%U' is read-only",
  				 tp->tp_name, name);
    done:
  	Py_XDECREF(descr);
  	Py_DECREF(name);
  	return res;
  }

  data descriptor -> obj dict -> non data descriptor
  详细的可以在python官网文档<https://docs.python.org/3/reference/datamodel.html#invoking-descriptors>查看.