#!/usr/bin/env python
# coding: utf-8

# > This is one of the 100 recipes of the [IPython Cookbook](http://ipython-books.github.io/), the definitive guide to high-performance scientific computing and data science in Python.
# 

# # 5.3. Wrapping a C library in Python with ctypes

# This example shows:
# 
#   * How to write and compile C code defining functions that are accessible from Python, and
#   * How to call C functions from Python using the native ctypes module.
#   
# This notebook has been written for Windows systems and Microsoft's C compiler (shipped with Visual Studio).

# **Note**: on Windows, for the C compiler to run, you need to execute a sequence of magic incantations before launching the IPython notebook. See the `_launch_notebook.bat` file in this repository.

# Let's write the generation of the Mandelbrot fractal in C.

# In[ ]:


get_ipython().run_cell_magic('writefile', 'mandelbrot.c', '\n// Needed when creating a DLL.\n#define EXPORT __declspec(dllexport)\n\n#include "stdio.h"\n#include "stdlib.h"\n\n// This function will be available in the DLL.\nEXPORT void __stdcall mandelbrot(int size,\n                                 int iterations,\n                                 int *col) \n{\n    // Variable declarations.\n    int i, j, n, index;\n    double cx, cy;\n    double z0, z1, z0_tmp, z0_2, z1_2;\n    \n    // Loop within the grid.\n    for (i = 0; i < size; i++)\n    {\n        cy = -1.5 + (double)i / size * 3;\n        for (j = 0; j < size; j++)\n        {\n            // We initialize the loop of the system.\n            cx = -2.0 + (double)j / size * 3;\n            index = i * size + j;\n            // Let\'s run the system.\n            z0 = 0.0;\n            z1 = 0.0;\n            for (n = 0; n < iterations; n++)\n            {\n                z0_2 = z0 * z0;\n                z1_2 = z1 * z1;\n                if (z0_2 + z1_2 <= 100)\n                {\n                    // Update the system.\n                    z0_tmp = z0_2 - z1_2 + cx;\n                    z1 = 2 * z0 * z1 + cy;\n                    z0 = z0_tmp;\n                    col[index] = n;\n                }\n                else\n                {\n                    break;\n                }\n            }\n        }\n    }\n}\n')


# Now, let's build this C source file into a DLL with Microsoft Visual Studio's `cl.exe`. The `/LD` option specifies that a DLL has to be created.

# In[ ]:


get_ipython().system('cl /LD mandelbrot.c')


# ## Wrapping the C library with NumPy and ctypes

# Let's access the library with ctypes.

# In[ ]:


import ctypes


# In[ ]:


lb = ctypes.CDLL('mandelbrot.dll')


# In[ ]:


lib = ctypes.WinDLL(None, handle=lb._handle)


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# Access the mandelbrot function.
mandelbrot = lib.mandelbrot


# NumPy and ctypes allow us to wrap the C function defined in the DLL.

# In[ ]:


from numpy.ctypeslib import ndpointer


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# Define the types of the output and arguments of this function.
mandelbrot.restype = None
mandelbrot.argtypes = [ctypes.c_int, ctypes.c_int,
                       ndpointer(ctypes.c_int)]


# Now, we can execute the mandelbrot function.

# In[ ]:


import numpy as np
# We initialize an empty array.
size = 200
iterations = 100
col = np.empty((size, size), dtype=np.int32)
# We execute the C function, which will update the array.
mandelbrot(size, iterations, col)


# The simulation has finished, let's display the fractal.

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import numpy as np
import matplotlib.pyplot as plt
get_ipython().run_line_magic('matplotlib', 'inline')


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plt.imshow(np.log(col), cmap=plt.cm.hot,);
plt.xticks([]);
plt.yticks([]);


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get_ipython().run_line_magic('timeit', 'mandelbrot(size, iterations, col)')


# We free the library handle at the end.

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lb._handle


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from ctypes.wintypes import HMODULE
ctypes.windll.kernel32.FreeLibrary.argtypes = [HMODULE]
ctypes.windll.kernel32.FreeLibrary(lb._handle);


# > You'll find all the explanations, figures, references, and much more in the book (to be released later this summer).
# 
# > [IPython Cookbook](http://ipython-books.github.io/), by [Cyrille Rossant](http://cyrille.rossant.net), Packt Publishing, 2014 (500 pages).