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https://github.com/eliben/pycparser

:snake: Complete C99 parser in pure Python
https://github.com/eliben/pycparser

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:snake: Complete C99 parser in pure Python

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README 

        
===============

pycparser v2.22

===============



.. image:: https://github.com/eliben/pycparser/workflows/pycparser-tests/badge.svg

  :align: center

  :target: https://github.com/eliben/pycparser/actions



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.. contents::

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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 with Python 3.8+ on Linux, macOS and Windows.



* **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 ``_



Note that **pycparser** (and PLY) uses docstrings for grammar specifications.

Python installations that strip docstrings (such as when using the Python

``-OO`` option) will fail to instantiate and use **pycparser**. You can try to

work around this problem by making sure the PLY parsing tables are pre-generated

in normal mode; this isn't an officially supported/tested mode of operation,

though.



Installation process

--------------------



The recommended way to install **pycparser** is with ``pip``::



    > pip install pycparser



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 for C11 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.



Note that the fake headers are not included in the ``pip`` package nor installed

via ``setup.py`` (`#224 `_).



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. Please note

that most realistic C code samples would require running the C preprocessor

before passing the code to **pycparser**; see the previous sections for more

details.



.. |examples| replace:: ``examples``

.. _examples: examples



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. This can be done by running

  the ``_build_tables.py`` script from the ``pycparser`` directory.

* 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.

  Note that these headers now include C11 code, so they may not work when the

  preprocessor is configured to an earlier C standard (like ``-std=c99``).



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.