[C++-sig] Accessing 2D array from python in C++

[alfa]

Hi John,

""



________________________________
 From: John Reid <j.reid at mail.cryst.bbk.ac.uk>
To: cplusplus-sig at python.org 
Sent: Wednesday, August 22, 2012 12:58 PM
Subject: Re: [C++-sig] Accessing 2D array from python in C++
 Hi John,

"You can call the expose_converters< npy_double >() function to expose
multiarrays of doubles to python as numpy arrays."

I'm afraid you understood that I have C++ array to be exposed as  numpy arrays in Python. My problem is actually the other way around, in which I have a 2D python array/matrix that I want to convert to/access in C++.

Thanks in advance.



On 22/08/12 11:45, alfa wrote:
> Hi John,
> 
> I'm sorry, I'm a bit confused because previously you said that the
> relevant implementation resides in
> "c++/myrrh/myrrh/python/multi_array_to_numpy.h"but now, you point to
> "src/python/man_module.cpp and src/python/multi_array_to_numpy.cpp".
> Hope you understand my problem of having 2D array in python that needs
> to be exposed/converted to C++. It would be great If I know any
> method/function that I can invoke from any of your implementations.
> 
> Thanks in advance.

Hi Alfa,

You can look at all of the code I've mentioned to work out how it works.
If it does not make sense perhaps it might be worth working through the
boost.python tutorial to get up to speed on how boost.python works.

You can call the expose_converters< npy_double >() function to expose
multiarrays of doubles to python as numpy arrays.

Please ask if you have any specific questions.

Regards,
John.


> 
> 
> ------------------------------------------------------------------------
> *From:* John Reid <j.reid at mail.cryst.bbk.ac.uk>
> *To:* cplusplus-sig at python.org
> *Sent:* Wednesday, August 22, 2012 12:28 PM
> *Subject:* Re: [C++-sig] Accessing 2D array from python in C++
> 
> On 22/08/12 11:13, alfa wrote:
>> Hi John,
>>
>> Thanks a lot for your implementation. In multi_array_to_numpy.h,  can
>> you give more hints on which method/function that I can possibly use if
>> I can include it in my implementation as a header file.
>>
>> Thanks in advance.
>>
> src/python/man_module.cpp and src/python/multi_array_to_numpy.cpp
> implement a boost.python module that exposes the multi-array classes.
> You have choose which data types you expose multiarrays for.
> 
> HTH,
> John.
> 
> 
>>
>> ------------------------------------------------------------------------
>> *From:* John Reid <j.reid at mail.cryst.bbk.ac.uk
> <mailto:j.reid at mail.cryst.bbk.ac.uk>>
>> *To:* cplusplus-sig at python.org <mailto:cplusplus-sig at python.org>
>> *Sent:* Thursday, August 16, 2012 5:02 PM
>> *Subject:* Re: [C++-sig] Accessing 2D array from python in C++
>>
>> If you don't mind digging around in my code, you could download the
>> source code for the STEME python package from pypi and look in the
>> c++/myrrh directory. There is code to access multi_arrays from python in
>> there.
>>
>> http://pypi.python.org/pypi/STEME/
>>
>> In particular the file
>> c++/myrrh/myrrh/python/multi_array_to_numpy.h contains the bulk of the
>> implementation.
>>
>> HTH,
>> John.
>>
>>
>>
>> On 16/08/12 09:29, alfa wrote:
>>> Hi,
>>>
>>> Could you give more hints on this or any code snippet that I can
>>> implement this. I'm a bit naive in applying this. Please consider my 2D
>>> array of Vp_cpp(Vp equivalent in Python) is as below:
>>>
>>>    typedef boost::multi_array<double, 2> array_type;
>>>    typedef array_type::index index;
>>>    array_type Vp_cpp(boost::extents[X_cpp][X_cpp]);
>>>
>>>
>>> I'm still puzzled how to "manually wrap the features" in the last
>> "..." in:
>>>    boost::python::class_< boost::multi_array<...> >(...)
>>>
>>> Thanks in advance.
>>>
>>> ------------------------------------------------------------------------
>>> *From:* Jim Bosch <talljimbo at gmail.com <mailto:talljimbo at gmail.com>
> <mailto:talljimbo at gmail.com <mailto:talljimbo at gmail.com>>>
>>> *To:* alfa <alfarobi0161 at yahoo.com <mailto:alfarobi0161 at yahoo.com>
> <mailto:alfarobi0161 at yahoo.com <mailto:alfarobi0161 at yahoo.com>>>
>>> *Cc:* Development of Python/C++ integration <cplusplus-sig at python.org
> <mailto:cplusplus-sig at python.org>
>> <mailto:cplusplus-sig at python.org <mailto:cplusplus-sig at python.org>>>
>>> *Sent:* Wednesday, August 15, 2012 5:34 PM
>>> *Subject:* Re: [C++-sig] Accessing 2D array from python in C++
>>>
>>> On Aug 15, 2012 1:57 AM, "alfa" <alfarobi0161 at yahoo.com
> <mailto:alfarobi0161 at yahoo.com>
>> <mailto:alfarobi0161 at yahoo.com <mailto:alfarobi0161 at yahoo.com>>
>>> <mailto:alfarobi0161 at yahoo.com <mailto:alfarobi0161 at yahoo.com>
> <mailto:alfarobi0161 at yahoo.com <mailto:alfarobi0161 at yahoo.com>>>> wrote:
>>>>
>>>> I apologize for double posting this because it was spammed before.
>>>>
>>>> Hi Jim,
>>>>
>>>> Do you mean, "you could wrap multi_array itself using class_", I
>>> should do as below:
>>>>
>>>> boost::python::class_<std::vector<std::vector<double> >
>>>>("PyVec").def(boost::python::vector_indexing_suite<std::vector<std::vector<double>
>>>> >());
>>>>
>>> No, I don't think that will work; I meant something like this:
>>> boost::python::class_< boost::multi_array<...> >(...)
>>>    ...;
>>> Where the last "..." is where you have to manually wrap the features of
>>> multi_array you want to use.  I'm afraid there's nothing as easy as
>>> vector_indexing_suite.
>>> Jim
>>>
>>>
>>>
>>>
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