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| 53 | <H1><A NAME="SECTION007400000000000000000"></A><A NAME="extending-with-embedding"></A> |
| 54 | <BR> |
| 55 | 5.4 Extending Embedded Python |
| 56 | |
| 57 | </H1> |
| 58 | |
| 59 | <P> |
| 60 | Until now, the embedded Python interpreter had no access to |
| 61 | functionality from the application itself. The Python API allows this |
| 62 | by extending the embedded interpreter. That is, the embedded |
| 63 | interpreter gets extended with routines provided by the application. |
| 64 | While it sounds complex, it is not so bad. Simply forget for a while |
| 65 | that the application starts the Python interpreter. Instead, consider |
| 66 | the application to be a set of subroutines, and write some glue code |
| 67 | that gives Python access to those routines, just like you would write |
| 68 | a normal Python extension. For example: |
| 69 | |
| 70 | <P> |
| 71 | <div class="verbatim"><pre> |
| 72 | static int numargs=0; |
| 73 | |
| 74 | /* Return the number of arguments of the application command line */ |
| 75 | static PyObject* |
| 76 | emb_numargs(PyObject *self, PyObject *args) |
| 77 | { |
| 78 | if(!PyArg_ParseTuple(args, ":numargs")) |
| 79 | return NULL; |
| 80 | return Py_BuildValue("i", numargs); |
| 81 | } |
| 82 | |
| 83 | static PyMethodDef EmbMethods[] = { |
| 84 | {"numargs", emb_numargs, METH_VARARGS, |
| 85 | "Return the number of arguments received by the process."}, |
| 86 | {NULL, NULL, 0, NULL} |
| 87 | }; |
| 88 | </pre></div> |
| 89 | |
| 90 | <P> |
| 91 | Insert the above code just above the <tt class="cfunction">main()</tt> function. |
| 92 | Also, insert the following two statements directly after |
| 93 | <tt class="cfunction">Py_Initialize()</tt>: |
| 94 | |
| 95 | <P> |
| 96 | <div class="verbatim"><pre> |
| 97 | numargs = argc; |
| 98 | Py_InitModule("emb", EmbMethods); |
| 99 | </pre></div> |
| 100 | |
| 101 | <P> |
| 102 | These two lines initialize the <code>numargs</code> variable, and make the |
| 103 | <tt class="function">emb.numargs()</tt> function accessible to the embedded Python |
| 104 | interpreter. With these extensions, the Python script can do things |
| 105 | like |
| 106 | |
| 107 | <P> |
| 108 | <div class="verbatim"><pre> |
| 109 | import emb |
| 110 | print "Number of arguments", emb.numargs() |
| 111 | </pre></div> |
| 112 | |
| 113 | <P> |
| 114 | In a real application, the methods will expose an API of the |
| 115 | application to Python. |
| 116 | |
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| 152 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> |
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