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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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