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<title>Pythonize class and libpythonize</title>
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</head>
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<body>
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<div class="NAVHEADER">
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<table summary="Footer navigation table" width="100%" border="0" cellpadding="0" cellspacing="0">
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<TR>
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<TH COLSPAN="3" ALIGN="center">Python Bindings for KDE (PyKDE-3.16.0)</TH>
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</TR>
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<tr>
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<td width="33%" align="left" valign="bottom">
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<a href="panapp5.html" accesskey="P" >Prev</a>
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</td>
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<td width="34%" align="center" valign="bottom"></td>
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<td width="33%" align="right" valign="bottom"></td>
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</tr>
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</table>
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</div>
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<hr align="LEFT" width="100%">
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<div align="center"><h1>Pythonize Class and libpythonize</h1></div>
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<p>
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libPythonize and the Pythonize class simplify embedding, loading and communicating with the Python
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interpreter. Pythonize is a class with methods for handling the interpreter and is included in libpythonize.
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Also in libpythonize is a C wrapper for the C++ Pythonize class. There is also a standalone C library
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libpythonizec, written completely in C. All 3 versions (C++, C and C wrapper) use the same methods/functions
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and the same args - the only major difference is in initialization and finalization.
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</p>
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<p>
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The method descriptions here apply to both C and C++ versions unless noted.
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</p>
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<p>
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Although libpythonize is used with (and installed with) PyKDE, it has no dependencies itself on
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PyKDE/KDE, PyTQt/TQt or sip. It does require qmake from TrollTech (part of TQt) to build.
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</p>
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<h2>Initialization and Finalization</h2>
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In C++, the interpreter is loaded and initialized using the Pythonize () constructor, which takes
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no arguments. In C, the initialize() function call accomplishes the same thing.
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The interpreter is finalized in C++ using the destructor ~Pythonize (). In C, the finalize() function
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accomplishes the same thing.
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<h2>Threading and Locking</h2>
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<p>
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Pythonize obtains the Python global interpreter lock when it initializes Python. It is currently the
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programmer's responsibility to release the lock when C++ accesses to the interpreter are complete. If
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the lock is not released, access will be denied to Python code relying on the interpreter (for example
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bindings like PyTQt or PyKDE).
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</p>
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<p>
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If a second instance of Pythonize is created (within the same parent process), that instance will actquire
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the lock automatically. In order to allow a second (and third or more) instance of Pythonize to be
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created and obtain the lock, it's necessary to have a related thread state (PyThreadState). This thread
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state is created by a call to PyThreadState_Get when the first instance of Pythonize is created. The
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thread state is stored in a global variable (declared in the cpp file) that is used by all subsequent
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instances of Pythonize. This means that applications using libpythonize are mormally single-threaded,
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at least in relation to the libpythonize interpreter instance. This is important for utilization with
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sip-based bindings like PyKDE and PyTQt.
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</p>
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<p>
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The global thread state is accessible via the getThreadState/setThreadState methods.
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</p>
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<h2>Methods/Functions</h2>
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<p>
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Methods are either called directly in C or as class members in C++. In C, int variables/values are
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used instead of bool.
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</p>
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<table border="0" bgcolor="#E0E0E0" width="100%">
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<tr>
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<td>
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<pre CLASS="PROGRAMLISTING">
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C++:
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Pythonize *pyize = Pythonize ();
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...
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bool result = pyize->appendToSysPath ("/usr/local/foo");
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C:
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initialize ();
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...
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int result = appendToSysPath ("/usr/local/foo");
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</pre>
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</td>
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</tr>
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</table>
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<hr>
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<h3>Pythonize () [C++] or initialize () [C]</h3>
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<p>
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Constructor/initializer - loads and initializaes the interpreter and actquires the global interpreter lock.
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Sets the value of pythonInit to <b>true</b> on success or <b>false</b> if construction/initialization fails
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Initializes the global thread state (first instance) or restores the global thread state (second and later
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instances). It is the programmer's resposibility to release the global interpreter lock to enable other
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code to access the interpreter. The lock and thread state are automatically actquired when any Pythonize
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instance is created..
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</p>
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<hr>
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<h3>bool getPythonInit ()</h3>
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<p>
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Returns the result of initializing/constructing the interpreter object. If the
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return value is <strong>true</strong>, the interpreter should be usable.
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If it returns <strong>false</strong>, an error occurred and the interpreter
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will not be useful. Most methods/functions check the value of pythonInit
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and won't run if it's <strong>false</strong>
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</p>
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<hr>
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<h3>~Pythonize () [C++] or finalize () [C]</h3>
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<p>
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Destructor/finalizer - shuts down the interpreter and destroys the class Sets pythonInit to <b>false</b>.
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</p>
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<hr>
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<h3>bool appendToSysPath (const char* newPath);</h3>
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<p>
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Appends newPath to sys.path
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</p>
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<hr>
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<h3>PyObject *importModule (char *moduleName);</h3>
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<p>
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Imports a module into the interpreter. Same as "import <moduleName>" in Python. moduleName
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must exist somewhere on sys.path. Returns a reference to the module imported. Returns <b>NULL</b> on failure.
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</p>
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<hr>
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<h3>PyObject *getNewObjectRef (PyObject *module, char *object)</h3>
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<p>
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Returns a reference to an object in an already loaded module (use importModule to load
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the module or get a reference to it) Returns <b>NULL</b> on failure.
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</p>
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<hr>
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<h3>PyObject *getSysModule ()</h3>
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<p>
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Returns a reference to the Python sys module. Returns <b>NULL</b> on failure.
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</p>
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<hr>
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<h3>PyObject *getMainModule ()</h3>
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<p>
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Returns a reference to the Python main module. Returns <b>NULL</b> on failure.
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</p>
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<hr>
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<h3>[internal] void *setMainModule ()</h3>
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<p>
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Sets internal value of main module
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</p>
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<hr>
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<h3>void decref (PyObject *object)</h3>
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<p>
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Uses Py_XDECREF to decrement the reference count of an object
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</p>
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<hr>
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<h3>bool runScript (char *scriptPath);</h3>
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<p>
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Runs an arbitrary script in the interpreter and returns Python's result.
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</p>
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<hr>
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<h3>bool runString (char *str);</h3>
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<p>
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Runs an arbitrary string in the interpreter (indentation required for mulit-line
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strings) and returns Python's result.
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</p>
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<hr>
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<h3>PyObject *runFunction (PyObject *object, PyObject *args);</h3>
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<p>
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If <em>object</em> is callable, runs <em>object</em> with <em>args</em> and
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returns the results of the function call as a PyObject. Returns <b>NULL</b> on failure.
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</p>
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<hr>
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<h3>void releaseLock ()</h3>
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<p>
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Releases the global interpreter lock using PyEval_SaveThread. Saves the global thread state.
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</p>
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<hr>
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<h3>void actquireLock ()</h3>
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<p>
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Actquires the global interpreter lock using PyEval_RestoreThread. Restores the global thread state.
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</p>
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<hr>
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<h3>PyThreadState *getThreadState ()</h3>
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<p>
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Retrieves the current value of the global thread state. Does not affect the global interpreter lock.
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</p>
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<hr>
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<h3>PyThreadState *setThreadState (PyThreadState *tstate)</h3>
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<p>
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Sets the global thread state to <i>tstate</i> and returns the previous global thread state. Does
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not affect the global interpreter lock.
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</p>
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<hr>
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<h2>Using libpythonize in an application</h2>
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<p>
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Include the pythonize.h header file (requires Python.h) and link to libpythonize.so - that's pretty much it. There are unit tests
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in both C and C++ in the pythonize/tests/ subdirectory. An example of libpythonize usage is in pykpanelapplet.cpp in the
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PyKDE distribution (pykpanelapplet/ directory).
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</p>
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<h2>Obtaining and building libpythonize</h2>
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<p>
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At present only the C++/C wrapper versions are available, and they're distributed with PyKDE.
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</p>
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<p>
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The build process for libpythonize uses TrollTech's qmake (available as part of TQt), but is simple enough
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to be included in most make files. See the pythonize.pro file for more information - most of the additional
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libs required are required by libpython, and may vary by platform.
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</p>
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<p>
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You can contact me at this address: <a href="mailto:jbublitz@nwinternet.com">Jim Bublitz <jbublitz@nwinternet.com></a>
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</p>
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<table summary="Footer navigation table" width="100%" border="0" cellpadding="0" cellspacing="0">
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<tr>
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<td width="33%" align="left" valign="top">
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<a href="panapp5.html" accesskey="P" >Prev</a>
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<td width="34%" align="center" valign="top">
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<a href="index.html" accesskey="H">Home</a>
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<td width="33%" align="left" valign="top">Applet Installer</td>
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<td width="34%" align="center" valign="top"> </td>
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<td width="33%" align="right" valign="top"></td>
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</tr>
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