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  2. pycparser

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================= pycparser v2.09.1 ================= :Author: `Eli Bendersky <http://eli.thegreenplace.net>`_ .. contents:: :backlinks: none .. sectnum:: Introduction ============ What is pycparser? ------------------ ``pycparser`` is a parser for the C language, written in pure Python. It is a module designed to be easily integrated into applications that need to parse C source code. What is it good for? -------------------- Anything that needs C code to be parsed. The following are some uses for ``pycparser``, taken from real user reports: * C code obfuscator * Front-end for various specialized C compilers * Static code checker * Automatic unit-test discovery * Adding specialized extensions to the C language ``pycparser`` is unique in the sense that it's written in pure Python - a very high level language that's easy to experiment with and tweak. To people familiar with Lex and Yacc, ``pycparser``'s code will be simple to understand. Which version of C does pycparser support? ------------------------------------------ ``pycparser`` aims to support the full C99 language (according to the standard ISO/IEC 9899). This is a new feature in the version 2.x series - earlier versions only supported C89. ``pycparser`` doesn't support any GCC extensions. See the `FAQ <https://bitbucket.org/eliben/pycparser/wiki/FAQ>`_ for more details. What grammar does pycparser follow? ----------------------------------- ``pycparser`` very closely follows the C grammar provided in the end of the C99 standard document How is pycparser licensed? -------------------------- `New BSD License <http://www.opensource.org/licenses/bsd-license.php>`_ Contact details --------------- Drop me an email to eliben@gmail.com for any questions regarding ``pycparser``. For reporting problems with ``pycparser`` or submitting feature requests, the best way is to open an issue on the `pycparser project page <https://bitbucket.org/eliben/pycparser/>`_. Installing ========== Prerequisites ------------- * ``pycparser`` was tested on Python 2.6, 2.7 and 3.2, on both Linux and Windows. It should work on any later version (in both the 2.x and 3.x lines) as well. ``pycparser`` has no external dependencies. The only non-stdlib library it uses is PLY, which is bundled in ``pycparser/ply``. The current PLY version is 3.4 Installation process -------------------- Installing ``pycparser`` is very simple. Once you download and unzip the package, you just have to execute the standard ``python setup.py install``. The setup script will then place the ``pycparser`` module into ``site-packages`` in your Python's installation library. Alternatively, since ``pycparser`` is listed in the `Python Package Index <http://pypi.python.org/pypi/pycparser>`_ (PyPI), you can install it using your favorite Python packaging/distribution tool, for example with:: > pip install pycparser It's recommended to run ``_build_tables.py`` in the ``pycparser`` code directory after installation to make sure the parsing tables are pre-generated. This can make your code run faster. Known problems -------------- * Some users who've installed a new version of ``pycparser`` over an existing version ran into a problem using the newly installed library. This has to do with parse tables staying around as ``.pyc`` files from the older version. If you see unexplained errors from ``pycparser`` after an upgrade, remove it (by deleting the ``pycparser`` directory in your Python's ``site-packages``, or wherever you installed it) and install again. Using ===== Interaction with the C preprocessor ----------------------------------- In order to be compilable, C code must be preprocessed by the C preprocessor - ``cpp``. ``cpp`` handles preprocessing directives like ``#include`` and ``#define``, removes comments, and does other minor tasks that prepare the C code for compilation. For all but the most trivial snippets of C code, ``pycparser``, like a C compiler, must receive preprocessed C code in order to function correctly. If you import the top-level ``parse_file`` function from the ``pycparser`` package, it will interact with ``cpp`` for you, as long as it's in your PATH, or you provide a path to it. On the vast majority of Linux systems, ``cpp`` is installed and is in the PATH. If you're on Windows and don't have ``cpp`` somewhere, you can use the one provided in the ``utils`` directory in ``pycparser``'s distribution. This ``cpp`` executable was compiled from the `LCC distribution <http://www.cs.princeton.edu/software/lcc/>`_, and is provided under LCC's license terms. What about the standard C library headers? ------------------------------------------ C code almost always includes various header files from the standard C library, like ``stdio.h``. While, with some effort, ``pycparser`` can be made to parse the standard headers from any C compiler, it's much simpler to use the provided "fake" standard includes in ``utils/fake_libc_include``. These are standard C header files that contain only the bare necessities to allow valid parsing of the files that use them. As a bonus, since they're minimal, it can significantly improve the performance of parsing large C files. The key point to understand here is that ``pycparser`` doesn't really care about the semantics of types. It only needs to know whether some token encountered in the source is a previously defined type. This is essential in order to be able to parse C correctly. See the ``using_cpp_libc.py`` example for more details. Basic usage ----------- Take a look at the ``examples`` directory of the distribution for a few examples of using ``pycparser``. These should be enough to get you started. Advanced usage -------------- The public interface of ``pycparser`` is well documented with comments in ``pycparser/c_parser.py``. For a detailed overview of the various AST nodes created by the parser, see ``pycparser/_c_ast.cfg``. There's also a `FAQ available here <https://bitbucket.org/eliben/pycparser/wiki/FAQ>`_. In any case, you can always drop me an `email <eliben@gmail.com>`_ for help. Modifying ========= There are a few points to keep in mind when modifying ``pycparser``: * The code for ``pycparser``'s AST nodes is automatically generated from a configuration file - ``_c_ast.cfg``, by ``_ast_gen.py``. If you modify the AST configuration, make sure to re-generate the code. * Make sure you understand the optimized mode of ``pycparser`` - for that you must read the docstring in the constructor of the ``CParser`` class. For development you should create the parser without optimizations, so that it will regenerate the Yacc and Lex tables when you change the grammar. Package contents ================ Once you unzip the ``pycparser`` package, you'll see the following files and directories: README.rst: This README file. setup.py: Installation script examples/: A directory with some examples of using ``pycparser`` pycparser/: The ``pycparser`` module source code. tests/: Unit tests. utils/cpp.exe: A Windows executable of the C pre-processor suitable for working with pycparser utils/fake_libc_include: Minimal standard C library include files that should allow to parse any C code. utils/internal/: Internal utilities for my own use. You probably don't need them. Contributors ============ Some people have contributed to ``pycparser`` by opening issues on bugs they've found and/or submitting patches. The list of contributors is at `this pycparser Wiki page <https://bitbucket.org/eliben/pycparser/wiki/Contributors>`_.