从C语言中读取类文件对象

从C语言中读取类文件对象：可以参考这篇文章： https://www.baidu.com/link?url=6djl4oF9q-bjXsKIc7n5xA5eoO3YbD_ISURCaytWx9o0B2dmmEhXclgxb_R

要读取一个类文件对象的数据，你需要重复调用 read() 方法，然后正确的解码获得的数据。

下面是一个C扩展函数例子，仅仅只是读取一个类文件对象中的所有数据并将其输出到标准输出：

#define CHUNK_SIZE 8192

/* Consume a "file-like" object and write bytes to stdout */
static PyObject *py_consume_file(PyObject *self, PyObject *args) {
  PyObject *obj;
  PyObject *read_meth;
  PyObject *result = NULL;
  PyObject *read_args;

  if (!PyArg_ParseTuple(args,"O", &obj)) {
    return NULL;
  }

  /* Get the read method of the passed object */
  if ((read_meth = PyObject_GetAttrString(obj, "read")) == NULL) {
    return NULL;
  }

  /* Build the argument list to read() */
  read_args = Py_BuildValue("(i)", CHUNK_SIZE);
  while (1) {
    PyObject *data;
    PyObject *enc_data;
    char *buf;
    Py_ssize_t len;

    /* Call read() */
    if ((data = PyObject_Call(read_meth, read_args, NULL)) == NULL) {
      goto final;
    }

    /* Check for EOF */
    if (PySequence_Length(data) == 0) {
      Py_DECREF(data);
      break;
    }

    /* Encode Unicode as Bytes for C */
    if ((enc_data=PyUnicode_AsEncodedString(data,"utf-8","strict"))==NULL) {
      Py_DECREF(data);
      goto final;
    }

    /* Extract underlying buffer data */
    PyBytes_AsStringAndSize(enc_data, &buf, &len);

    /* Write to stdout (replace with something more useful) */
    write(1, buf, len);

    /* Cleanup */
    Py_DECREF(enc_data);
    Py_DECREF(data);
  }
  result = Py_BuildValue("");

 final:
  /* Cleanup */
  Py_DECREF(read_meth);
  Py_DECREF(read_args);
  return result;
}
要测试这个代码，先构造一个类文件对象比如一个StringIO实例，然后传递进来：

>>> import io
>>> f = io.StringIO('Hello\nWorld\n')
>>> import sample
>>> sample.consume_file(f)
Hello
World
>>>