大型网站开发收费,网络seo排名,找个不能粘贴文字的网站做实验,购物网站的搜索框用代码怎么做在上一节中#xff0c;讨论了在用C语言扩展Python模块时#xff0c;应该如何处理无处不在的引用计数问题。重点关注的是在实现一个C Python的函数时#xff0c;对于一个PyObject对象#xff0c;何时调用Py_INCREF和Py_DECREF。在编写C语言代码时#xff0c;需要了解Python…在上一节中讨论了在用C语言扩展Python模块时应该如何处理无处不在的引用计数问题。重点关注的是在实现一个C Python的函数时对于一个PyObject对象何时调用Py_INCREF和Py_DECREF。在编写C语言代码时需要了解Python提供的C/C API的实现细节特别是有的API内部实现会调用Py_INCREF这时自己编写的函数可能需要调用Py_DECREF而有的API内部实现只是borrowed reference此时一般不应该调用Py_DECREF。本节讨论在C扩展Python时如何对异常和错误进行处理。Python解释器的实现中有一个重要的约定当一个函数失败它应该设置一个exception condition并返回一个错误值(通常是NULl指针)。异常是存放在解释器的一个全局变量中如果这个变量是NULL那么没有异常发生。另外一个全局变量存放的是跟异常相关的值还有一个变量包含了stack traceback记录了产生错误时的Python Code。这三个变量对应Python的sys模块的三个变量sys.exc_type, sys.exc_value, sys.exc_traceback。在1.5版本之后这三个变量用exc_info()代替了。这三个全局的变量在C Python 源码中是存放在PyThreadState *_PyThreadState_Current这个结构体中的 而_PyThreadState_Current是在pythonrun.c的Py_InitializeEx中初始化的。PyThreadState结构体定义红色框中的三个变量就是error indicator。常见的Python设置异常的接口Python API定义了一系列的function来设置不同类型的异常定义在Python源码中的Python/error.c中。PyErr_SetString:最常用的莫过于PyErr_SetString函数的原型为函数的作用是设置Python解释器的全局error indicator。参数分别为一个exception对象和一个描述异常的字符串。exception object通常是一个已经定义好的object 不需要增加它的引用计数在PyErr_SetString源码中已经调用了Py_XINCREF(exception)。/*Predefined exceptions*/PyAPI_DATA(PyObject*) PyExc_BaseException;PyAPI_DATA(PyObject*) PyExc_Exception;PyAPI_DATA(PyObject*) PyExc_StopIteration;PyAPI_DATA(PyObject*) PyExc_GeneratorExit;PyAPI_DATA(PyObject*) PyExc_StandardError;PyAPI_DATA(PyObject*) PyExc_ArithmeticError;PyAPI_DATA(PyObject*) PyExc_LookupError;PyAPI_DATA(PyObject*) PyExc_AssertionError;PyAPI_DATA(PyObject*) PyExc_AttributeError;PyAPI_DATA(PyObject*) PyExc_EOFError;PyAPI_DATA(PyObject*) PyExc_FloatingPointError;PyAPI_DATA(PyObject*) PyExc_EnvironmentError;PyAPI_DATA(PyObject*) PyExc_IOError;PyAPI_DATA(PyObject*) PyExc_OSError;PyAPI_DATA(PyObject*) PyExc_ImportError;PyAPI_DATA(PyObject*) PyExc_IndexError;PyAPI_DATA(PyObject*) PyExc_KeyError;PyAPI_DATA(PyObject*) PyExc_KeyboardInterrupt;PyAPI_DATA(PyObject*) PyExc_MemoryError;PyAPI_DATA(PyObject*) PyExc_NameError;PyAPI_DATA(PyObject*) PyExc_OverflowError;PyAPI_DATA(PyObject*) PyExc_RuntimeError;PyAPI_DATA(PyObject*) PyExc_NotImplementedError;PyAPI_DATA(PyObject*) PyExc_SyntaxError;PyAPI_DATA(PyObject*) PyExc_IndentationError;PyAPI_DATA(PyObject*) PyExc_TabError;PyAPI_DATA(PyObject*) PyExc_ReferenceError;PyAPI_DATA(PyObject*) PyExc_SystemError;PyAPI_DATA(PyObject*) PyExc_SystemExit;PyAPI_DATA(PyObject*) PyExc_TypeError;PyAPI_DATA(PyObject*) PyExc_UnboundLocalError;PyAPI_DATA(PyObject*) PyExc_UnicodeError;PyAPI_DATA(PyObject*) PyExc_UnicodeEncodeError;PyAPI_DATA(PyObject*) PyExc_UnicodeDecodeError;PyAPI_DATA(PyObject*) PyExc_UnicodeTranslateError;PyAPI_DATA(PyObject*) PyExc_ValueError;PyAPI_DATA(PyObject*) PyExc_ZeroDivisionError;PyErr_SetObject:从PyErr_SetString实现的源码中可以看到内部调用了PyErr_SetObject, PyErr_SetObject内部又调用了PyErr_Restore。PyErr_SetObject函数原型是PyObject* PyErr_Occurred():函数返回当前是否有异常发生如果有返回current exception object【borrowed reference】否则返回NULLint PyErr_ExceptionMatches(PyObject* exc)int PyErr_GivenExceptionMatches(PyObject* given, PyObject* exc):判断给定的异常对象是否符合exc类型。PyErr_Clear():清除Python解释器的error indicator。Python解释器不会检测到有异常发生。PyErr_Fetch(PyObject** ptype, PyObject** pvalue, PyObject** ptraceback)获得error indicator的三个变量如果error indicator没有设置ptype, pvalue, ptraceback都被设置为NULL。error indicator会被置空将三个变量的地址赋给ptype, pvalue, ptraceback。PyErr_Restore(PyObject* type, PyObject* value, PyObject* traceback)使用给定的三个变量设置error indicator。代码中使用异常接口的规则如果函数f调用函数g其中g函数失败应该怎样设置异常呢通常的做法是在g中调用设置异常的各个接口比如PyErr_SetString通知Python解释器有异常发生了函数g然后返回一个NULL给函数f而f不用再处理异常因为函数g已经上报过了。比如我们自己写的函数调用了PyArg_ParseTuple(),这个函数出现错误时返回NULL但是我们不用自己上报异常异常的上报由PyArg_ParseTuple本身处理。一旦通过PyErr_SetString设置了异常那么Python解释器在主循环中检测到error indicator被设置会暂停执行当前的Python Code会试图寻找exception handler来处理异常。Python源码中使用异常处理接口的例子PyTuple_GetItemPyObject *PyTuple_GetItem(register PyObject*op, register Py_ssize_t i){if (!PyTuple_Check(op)) {PyErr_BadInternalCall();returnNULL;}if (i 0 || i Py_SIZE(op)) {//如果索引有错误设置异常PyErr_SetString(PyExc_IndexError, tuple index out of range);returnNULL;}return ((PyTupleObject *)op) -ob_item[i];}PyErr_SetString实现voidPyErr_SetString(PyObject*exception, const char *string){PyObject*value PyString_FromString(string);PyErr_SetObject(exception, value);Py_XDECREF(value);}PyErr_SetObject实现voidPyErr_SetObject(PyObject*exception, PyObject *value){Py_XINCREF(exception);//增加引用计数Py_XINCREF(value); //增加引用计数PyErr_Restore(exception, value, (PyObject *)NULL);}PyErr_Restore实现voidPyErr_Restore(PyObject*type, PyObject *value, PyObject *traceback){PyThreadState*tstate PyThreadState_GET();PyObject*oldtype, *oldvalue, *oldtraceback;if (traceback ! NULL !PyTraceBack_Check(traceback)) {/*XXX Should never happen -- fatal error instead?*//*Well, it could be None.*/Py_DECREF(traceback);tracebackNULL;}/*Save these in locals to safeguard against recursiveinvocation through Py_XDECREF*/oldtype tstate-curexc_type;oldvalue tstate-curexc_value;oldtraceback tstate-curexc_traceback;//设置当前的异常tstate-curexc_type type;tstate-curexc_value value;tstate-curexc_traceback traceback;//旧的异常变量需要减少引用计数Py_XDECREF(oldtype);Py_XDECREF(oldvalue);Py_XDECREF(oldtraceback);}自定义异常除了使用Python已经定义好的异常对象之外我们可以自定义异常类型主要是通过PyErr_NewException创建一个异常对象。1. 在文件头部定义一个static 变量static PyObject *MyError;2. 在模块初始化时传入我们自定义的异常对象PyMODINIT_FUNCinittest(void){PyObject*m;m Py_InitModule(test, TestMethods);if (m NULL)return;MyError PyErr_NewException(test.error, NULL, NULL);Py_INCREF(MyError);PyModule_AddObject(m,error,MyError);}3. 在通过PyErr_SetString设置异常时第一个参数传入MyError即可。
