From daniele at grinta.net  Tue Jun 16 16:32:47 2020
From: daniele at grinta.net (Daniele Nicolodi)
Date: Tue, 16 Jun 2020 14:32:47 -0600
Subject: [Cython] Most efficient way to create an object with Python C-API
Message-ID: <9788e088-8893-c53a-0e3a-fed8f82f072e@grinta.net>

Hello,

this is not a question directly related to cython, but I think the
readers of this list may have the right expertise to answer it.

I am working on a Python extension where I need to instantiate a lot of
Decimal objects. I would like to make it as efficient as possible.
Unfortunately the C-API of the _decimal module is not exposed (as is for
example done for the datetime module).

The straightforward approach is something on the lines of:

PyObject* decimal = PyImport_ImportModule("decimal");
PyObject* constructor = PyObject_GetAttrString(m, "Decimal");

and then instantiate the objects with something like:

PyObject* obj = PyObject_CallFunction(PyDec_Type, "s#", str, len);

Is there a better way?

I was thinking about getting to the PyTypeObject for Decimal, like

PyTypeObject* type = Py_TYPE(obj);

but then I don't see an easy way to use it to instantiate an object.

Am I missing something?

Thank you.

Cheers,
Dan

From greg.ewing at canterbury.ac.nz  Wed Jun 17 18:10:18 2020
From: greg.ewing at canterbury.ac.nz (Greg Ewing)
Date: Thu, 18 Jun 2020 10:10:18 +1200
Subject: [Cython] Most efficient way to create an object with Python
 C-API
In-Reply-To: <9788e088-8893-c53a-0e3a-fed8f82f072e@grinta.net>
References: <9788e088-8893-c53a-0e3a-fed8f82f072e@grinta.net>
Message-ID: <14aecc99-8def-e5cb-e2b7-d312dd6f557e@canterbury.ac.nz>

On 17/06/20 8:32 am, Daniele Nicolodi wrote:
> PyObject* decimal = PyImport_ImportModule("decimal");
> PyObject* constructor = PyObject_GetAttrString(m, "Decimal");
> PyObject* obj = PyObject_CallFunction(PyDec_Type, "s#", str, len);
> 
> Is there a better way?
> 
> I was thinking about getting to the PyTypeObject for Decimal, like
> 
> PyTypeObject* type = Py_TYPE(obj);

That will get you exactly the same object you get by importing
the decimal.Decimal class. In Python3 there is no difference
between a type and a class. So I don't think there's any
substantially faster way.

-- 
Greg