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  3. <title>SWIG:Examples:python:simple</title>
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  9. <tt>SWIG/Examples/python/simple/</tt>
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  11. 

  12. <H2>Simple Python Example</H2>
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  14. <p>
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  15. This example illustrates how you can hook Python to a very simple C program containing
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  16. a function and a global variable.
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  17. 

  18. <h2>The C Code</h2>
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  19. 

  20. Suppose you have the following C code:
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  22. <blockquote>
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  23. <pre>
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  24. /* File : example.c */
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  26. /* A global variable */
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  27. double Foo = 3.0;
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  29. /* Compute the greatest common divisor of positive integers */
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  30. int gcd(int x, int y) {
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  31.   int g;
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  32.   g = y;
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  33.   while (x &gt; 0) {
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  34.     g = x;
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  35.     x = y % x;
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  36.     y = g;
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  37.   }
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  38.   return g;
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  39. }
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  40. </pre>
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  41. </blockquote>
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  42. 

  43. <h2>The SWIG interface</h2>
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  44. 

  45. Here is a simple SWIG interface file:
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  47. <blockquote>
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  48. <pre>
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  49. /* File: example.i */
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  50. %module example
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  51. 

  52. extern int gcd(int x, int y);
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  53. extern double Foo;
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  54. </pre>
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  55. </blockquote>
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  56. 

  57. <h2>Compilation</h2>
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  59. <ol>
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  60. <li><tt>swig -python <a href="example.i">example.i</a></tt>
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  61. <p>
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  62. <li>Compile <tt><a href="example_wrap.c">example_wrap.c</a></tt> and <tt><a href="example.c">example.c</a></tt>
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  63. to create the extension <tt>examplemodule.so</tt>. 
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  64. </ol>
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  65. 

  66. <h2>Using the extension</h2>
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  67. 

  68. Click <a href="example.py">here</a> to see a script that calls our C functions from Python.
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  69. 

  70. <h2>Key points</h2>
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  72. <ul>
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  73. <li>Use the <tt>import</tt> statement to load your extension module from Python. For example:
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  74. <blockquote>
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  75. <pre>
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  76. import example
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  77. </pre>
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  78. </blockquote>
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  79. 

  80. <li>C functions work just like Python functions. For example:
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  81. <blockquote>
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  82. <pre>
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  83. g = example.gcd(42,105)
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  84. </pre>
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  85. </blockquote>
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  86. 

  87. <li>C global variables are accessed through a special variable called 'cvar'. For example:
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  88. <blockquote>
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  89. <pre>
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  90. a = example.cvar.Foo
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  91. </pre>
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  92. </blockquote>
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  93. </ul>
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  95. <hr>
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  96. </body>
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  97. </html>
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