projects / OpenSPARC-T2-DV / blame
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| 16 | <title>1.4 Embedding Python </title> | |
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| 53 | ||
| 54 | <H1><A NAME="SECTION003400000000000000000"></A><A NAME="embedding"></A> | |
| 55 | <BR> | |
| 56 | 1.4 Embedding Python | |
| 57 | </H1> | |
| 58 | ||
| 59 | <P> | |
| 60 | The one important task that only embedders (as opposed to extension | |
| 61 | writers) of the Python interpreter have to worry about is the | |
| 62 | initialization, and possibly the finalization, of the Python | |
| 63 | interpreter. Most functionality of the interpreter can only be used | |
| 64 | after the interpreter has been initialized. | |
| 65 | ||
| 66 | <P> | |
| 67 | The basic initialization function is | |
| 68 | <tt class="cfunction">Py_Initialize()</tt><a id='l2h-30' xml:id='l2h-30'></a>. | |
| 69 | This initializes the table of loaded modules, and creates the | |
| 70 | fundamental modules <tt class="module">__builtin__</tt><a id='l2h-31' xml:id='l2h-31'></a>, | |
| 71 | <tt class="module">__main__</tt><a id='l2h-32' xml:id='l2h-32'></a>, <tt class="module">sys</tt><a id='l2h-33' xml:id='l2h-33'></a>, | |
| 72 | and <tt class="module">exceptions</tt>.<a id='l2h-34' xml:id='l2h-34'></a> It also initializes | |
| 73 | the module search path (<code>sys.path</code>).<a id='l2h-27' xml:id='l2h-27'></a><a id='l2h-29' xml:id='l2h-29'></a> | |
| 74 | <P> | |
| 75 | <tt class="cfunction">Py_Initialize()</tt> does not set the ``script argument list'' | |
| 76 | (<code>sys.argv</code>). If this variable is needed by Python code that | |
| 77 | will be executed later, it must be set explicitly with a call to | |
| 78 | <code>PySys_SetArgv(<var>argc</var>, | |
| 79 | <var>argv</var>)</code><a id='l2h-35' xml:id='l2h-35'></a> subsequent to the call to | |
| 80 | <tt class="cfunction">Py_Initialize()</tt>. | |
| 81 | ||
| 82 | <P> | |
| 83 | On most systems (in particular, on <span class="Unix">Unix</span> and Windows, although the | |
| 84 | details are slightly different), | |
| 85 | <tt class="cfunction">Py_Initialize()</tt> calculates the module search path based | |
| 86 | upon its best guess for the location of the standard Python | |
| 87 | interpreter executable, assuming that the Python library is found in a | |
| 88 | fixed location relative to the Python interpreter executable. In | |
| 89 | particular, it looks for a directory named | |
| 90 | <span class="file">lib/python2.4</span> relative to the parent directory where | |
| 91 | the executable named <span class="file">python</span> is found on the shell command | |
| 92 | search path (the environment variable <a class="envvar" id='l2h-36' xml:id='l2h-36'>PATH</a>). | |
| 93 | ||
| 94 | <P> | |
| 95 | For instance, if the Python executable is found in | |
| 96 | <span class="file">/usr/local/bin/python</span>, it will assume that the libraries are in | |
| 97 | <span class="file">/usr/local/lib/python2.4</span>. (In fact, this particular path | |
| 98 | is also the ``fallback'' location, used when no executable file named | |
| 99 | <span class="file">python</span> is found along <a class="envvar" id='l2h-37' xml:id='l2h-37'>PATH</a>.) The user can override | |
| 100 | this behavior by setting the environment variable <a class="envvar" id='l2h-38' xml:id='l2h-38'>PYTHONHOME</a>, | |
| 101 | or insert additional directories in front of the standard path by | |
| 102 | setting <a class="envvar" id='l2h-39' xml:id='l2h-39'>PYTHONPATH</a>. | |
| 103 | ||
| 104 | <P> | |
| 105 | The embedding application can steer the search by calling | |
| 106 | <code>Py_SetProgramName(<var>file</var>)</code><a id='l2h-40' xml:id='l2h-40'></a> <em>before</em> calling | |
| 107 | <tt class="cfunction">Py_Initialize()</tt>. Note that <a class="envvar" id='l2h-41' xml:id='l2h-41'>PYTHONHOME</a> still | |
| 108 | overrides this and <a class="envvar" id='l2h-42' xml:id='l2h-42'>PYTHONPATH</a> is still inserted in front of | |
| 109 | the standard path. An application that requires total control has to | |
| 110 | provide its own implementation of | |
| 111 | <tt class="cfunction">Py_GetPath()</tt><a id='l2h-43' xml:id='l2h-43'></a>, | |
| 112 | <tt class="cfunction">Py_GetPrefix()</tt><a id='l2h-44' xml:id='l2h-44'></a>, | |
| 113 | <tt class="cfunction">Py_GetExecPrefix()</tt><a id='l2h-45' xml:id='l2h-45'></a>, and | |
| 114 | <tt class="cfunction">Py_GetProgramFullPath()</tt><a id='l2h-46' xml:id='l2h-46'></a> (all | |
| 115 | defined in <span class="file">Modules/getpath.c</span>). | |
| 116 | ||
| 117 | <P> | |
| 118 | Sometimes, it is desirable to ``uninitialize'' Python. For instance, | |
| 119 | the application may want to start over (make another call to | |
| 120 | <tt class="cfunction">Py_Initialize()</tt>) or the application is simply done with its | |
| 121 | use of Python and wants to free all memory allocated by Python. This | |
| 122 | can be accomplished by calling <tt class="cfunction">Py_Finalize()</tt>. The function | |
| 123 | <tt class="cfunction">Py_IsInitialized()</tt><a id='l2h-47' xml:id='l2h-47'></a> returns | |
| 124 | true if Python is currently in the initialized state. More | |
| 125 | information about these functions is given in a later chapter. | |
| 126 | ||
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| 131 | <tr> | |
| 132 | <td class='online-navigation'><a rel="prev" title="1.3 Exceptions" | |
| 133 | href="exceptions.html"><img src='../icons/previous.png' | |
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| 137 | border='0' height='32' alt='Up One Level' width='32' /></A></td> | |
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| 152 | <b class="navlabel">Previous:</b> | |
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| 161 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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