[Python-Dev] cpython: PyUnicode_FromKindAndData() raises a ValueError if the kind is unknown

[Victor Stinner]

> > -    assert(0);
> > +    PyErr_SetString(PyExc_ValueError, "invalid kind");
> > 
> >      return NULL;
> >  
> >  }
> 
> Is that really a ValueError? It should only be a ValueError if the user
> could trigger that error. Otherwise it should be a SystemError.

You are right, ValueError is not best exception here. I used SystemError 
instead: see my commit 721bb2e59815.

PyUnicode_FromFormat() does still use ValueError in PyUnicode_FromFormatV:

PyErr_SetString(PyExc_ValueError,
    "incomplete format key");

PyErr_SetString(PyExc_ValueError,
    "width too big");

PyErr_SetString(PyExc_ValueError,
    "prec too big");

PyErr_SetString(PyExc_ValueError,
    "incomplete format");

PyErr_Format(PyExc_ValueError,
    "unsupported format character '%c' (0x%x) "
    "at index %zd",
    (31<=c && c<=126) ? (char)c : '?',
    (int)c,
    fmtpos - 1);

PyErr_Format(PyExc_ValueError,
    "PyUnicode_FromFormatV() expects an ASCII-encoded format "
    "string, got a non-ASCII byte: 0x%02x",
    (unsigned char)*f);

Should we also replace them by SystemError? It might break backward 
compatibility, but I do really hope that nobody relies on these errors ;-)

Victor