=============== pycparser v2.18 =============== :Author: `Eli Bendersky `_ .. 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 One of the most popular uses of **pycparser** is in the `cffi `_ library, which uses it to parse the declarations of C functions and types in order to auto-generate FFIs. **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. It also has no external dependencies (except for a Python interpreter), making it very simple to install and deploy. Which version of C does pycparser support? ------------------------------------------ **pycparser** aims to support the full C99 language (according to the standard ISO/IEC 9899). Some features from C11 are also supported, and patches to support more are welcome. **pycparser** supports very few GCC extensions, but it's fairly easy to set things up so that it parses code with a lot of GCC-isms successfully. See the `FAQ `_ for more details. What grammar does pycparser follow? ----------------------------------- **pycparser** very closely follows the C grammar provided in Annex A of the C99 standard (ISO/IEC 9899). How is pycparser licensed? -------------------------- `BSD license `_. Contact details --------------- For reporting problems with **pycparser** or submitting feature requests, please open an `issue `_, or submit a pull request. Installing ========== Prerequisites ------------- * **pycparser** was tested on Python 2.7, 3.4 and 3.5, 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 3.10, retrieved from ``_ 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 `_ (PyPI), you can install it using your favorite Python packaging/distribution tool, for example with:: > pip install pycparser 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 performs 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. Note also that you can use ``gcc -E`` or ``clang -E`` instead of ``cpp``. See the ``using_gcc_E_libc.py`` example for more details. Windows users can download and install a binary build of Clang for Windows `from this website `_. What about the standard C library headers? ------------------------------------------ C code almost always ``#include``\s 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 `this blog post `_ 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 `_. In any case, you can always drop me an `email `_ 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. LICENSE: The pycparser license setup.py: Installation script examples/: A directory with some examples of using **pycparser** pycparser/: The **pycparser** module source code. tests/: Unit tests. 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 in the CONTRIBUTORS file in the source distribution. After **pycparser** moved to Github I stopped updating this list because Github does a much better job at tracking contributions. CI Status ========= **pycparser** has automatic testing enabled through the convenient `Travis CI project `_. Here is the latest build status: .. image:: https://travis-ci.org/eliben/pycparser.png?branch=master :align: center :target: https://travis-ci.org/eliben/pycparser AppVeyor also helps run tests on Windows: .. image:: https://ci.appveyor.com/api/projects/status/wrup68o5y8nuk1i9?svg=true :align: center :target: https://ci.appveyor.com/project/eliben/pycparser/