GeezerVison

Python 3.9.2 (default, Feb 28 2021, 17:03:44) 
[GCC 10.2.1 20210110] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import io
>>> d = io.IncrementalNewlineDecoder(None, translate=True)
>>> d.decode('str')
'str'
>>> d.decode(b'bytes')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: decoder should return a string result, not 'bytes'

PyObject *
_PyIncrementalNewlineDecoder_decode(PyObject *myself,
                                    PyObject *input, int final)
{
    PyObject *output;
    Py_ssize_t output_len;
    nldecoder_object *self = (nldecoder_object *) myself;

    if (self->decoder == NULL) {
        PyErr_SetString(PyExc_ValueError,
                        "IncrementalNewlineDecoder.__init__ not called");
        return NULL;
    }

    /* decode input (with the eventual \r from a previous pass) */
    if (self->decoder != Py_None) {
        output = PyObject_CallMethodObjArgs(self->decoder,
            &_Py_ID(decode), input, final ? Py_True : Py_False, NULL);
    }
    else {
        output = input;
        Py_INCREF(output);
    }

    if (check_decoded(output) < 0)
        return NULL;

    /* ... */