On Tue, Feb 24, 2009 at 15:04, Matthew Brett <matthew.brett@gmail.com> wrote:

Hi,

I was just trying to write a docstring for np.dtype.isbuiltin, when I realized I didn't understand it.

As far as I can see, isbuitin should return:

0 for structured array dtypes 1 for types compiled into numpy 2 for extension types using the numpy C-API type extension machinery.

Here's the C code:

static PyObject * arraydescr_isbuiltin_get(PyArray_Descr *self) {    long val;    val = 0;    if (self->fields == Py_None) val = 1;    if (PyTypeNum_ISUSERDEF(self->type_num)) val = 2;    return PyInt_FromLong(val); }

But, why is this?

In [2]: dt = np.dtype('S1')

In [3]: dt Out[3]: dtype('|S1')

In [4]: dt.isbuiltin Out[4]: 0

In [5]: print dt.fields None

In [6]: print dt.fields == None True

Same for np.dtype('U1')

The variable-length string dtypes are not builtin. The user-defined lengths make them user-defined dtypes. If you want a real kick in the pants, try playing with dtype(str). And then try eval'ing its repr. -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco