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Let me start with a disclaimer that i'm putting this question after lot of research and not finding any direct and step by step example.

Have gone through Cython , SWIG, Boostpython documentation but couldn't get a step by step process and so posting here -

I have a .cpp & .h file with couple of mathematical functions defined.I want to call them in a python (.py) code file.

How do i integrate?Which is the best and neatest way to go about it. Please illustrate

raul
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  • Most people would consider [this](http://www.swig.org/tutorial.html) and [this](http://www.boost.org/doc/libs/1_57_0/libs/python/doc/tutorial/doc/html/index.html) to be step by step guides to SWIG and Boost.Python, respectively. What exactly do you need that these don't provide? – Marcelo Cantos Mar 03 '15 at 12:18
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    This [post][1] seems to answer your question by using library ctypes. [1]:http://stackoverflow.com/questions/145270/calling-c-c-from-python – maeVeyable Mar 03 '15 at 12:55
  • "Best" is subjective. For simple code, just make sure your cpp code has a C interface (extern "C") and use ctypes. Just look at the official docs for ctypes. – Jagoly Mar 03 '15 at 16:19
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    Please, add an example of one function of yours, it will become easier to propose how to do it... – Saullo G. P. Castro Mar 04 '15 at 01:10
  • Trying to do it via Cython – raul Mar 04 '15 at 11:03

2 Answers2

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See this part of the Cython documentation; it takes you step-by-step through interfacing with a C library.

Liam Marshall
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1

Since i eventually solved it using some of the help provided here and research , let me post the answer.

I did the import of CPP function via Python using Cython.

Cython wraps the Python code with CPP file and compiles the two. The outcome is a Python module (name of the module can be specified in setup.py file ) and the module can be called as usual.

The issue i was facing was calling a CPP function from Python.So here are my tips for working it out

  1. Define your function in C++ Header and CPP file.
  2. Using cdef , define the function in Python script in the beginning where you import modules define other variables.This definition is similar to C++ header file definition
  3. While pasing arguments and arrays to the function call from python , ensure all variables and arrays are type casted as CPP.
  4. For arrays, it is a bit tricky. E.G. a double array in Python can be type casted using array.array(array_to_cast). In the following example, we cast the python array, dev, into the c++ array, dev_arr. Note that dev is an array of type double in python, hence the first parameter input to array.array() is 'd'. 
cdef array.array dev_arr = array.array('d',dev)

While passing the dev_arr array to your main CPP function, you have to specify this array :data.as_doubles 

fn_response = cpp_fn_call(stddev_arr.data.as_doubles,...)

Rest will work smoothly.

RPeters
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raul
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