15.17 传递文件名给C扩展

## 问题 You need to pass filenames to C library functions, but need to make sure the filenamehas been encoded according to the system’s expected filename encoding. ## 解决方案 To write an extension function that receives a filename, use code such as this: static PyObject [*](#)py_get_filename(PyObject [*](#)self, PyObject [*](#)args) { PyObject [*](#)bytes;char [*](#)filename;Py_ssize_t len;if (!PyArg_ParseTuple(args,”O&”, PyUnicode_FSConverter, &bytes)) { > return NULL; }PyBytes_AsStringAndSize(bytes, &filename, &len);/* Use filename [*](#)/... /* Cleanup and return [*](#)/Py_DECREF(bytes)Py_RETURN_NONE; } If you already have a PyObject * that you want to convert as a filename, use code suchas the following: PyObject _obj; /_ Object with the filename [*](#)/PyObject [*](#)bytes;char [*](#)filename;Py_ssize_t len; bytes = PyUnicode_EncodeFSDefault(obj);PyBytes_AsStringAndSize(bytes, &filename, &len);/* Use filename [*](#)/... /* Cleanup [*](#)/Py_DECREF(bytes); If you need to return a filename back to Python, use the following code: /* Turn a filename into a Python object [*](#)/ char _filename; /_ Already set _/int filename_len; /_ Already set [*](#)/ PyObject [*](#)obj = PyUnicode_DecodeFSDefaultAndSize(filename, filename_len); ## 讨论 Dealing with filenames in a portable way is a tricky problem that is best left to Python.If you use this recipe in your extension code, filenames will be handled in a manner thatis consistent with filename handling in the rest of Python. This includes encoding/decoding of bytes, dealing with bad characters, surrogate escapes, and other complica‐tions.