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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.
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>`_.
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