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eliben/pycparser

A complete C99/C11 parser written in pure Python, producing an AST from C source code with no external dependencies.

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What is it?

pycparser parses C source code and builds an abstract syntax tree (AST) that Python programs can traverse and modify. It follows the C grammar from Annex A of the C99 standard and aims to cover C11, with C23 support available through a dialect setting. It is implemented in pure Python with no dependencies beyond the interpreter, so it installs easily with pip.

Because C code usually needs preprocessing first, pycparser can call an external preprocessor such as cpp, gcc -E, or clang -E, either through its parse_file function or by passing already preprocessed code. It also ships minimal fake standard library headers in utils/fake_libc_include to speed up parsing of files that include system headers.

The project is widely used as a component in other tools, most notably the cffi library, which relies on it to read C function and type declarations.

Key features

  • 01Parses C99 and C11 source, with C23 available via a dialect option.
  • 02Written in pure Python with no external dependencies.
  • 03Produces an AST whose node types are documented in _c_ast.cfg.
  • 04Works with an external preprocessor such as cpp, gcc -E, or clang -E.
  • 05Includes minimal fake libc headers for faster parsing of code with standard includes.

Use cases

  • Building a static code checker or linter for C code.
  • Writing source-to-source transformations or obfuscators for C.
  • Adding custom extensions to the C language through AST rewriting.
  • Generating FFI bindings by parsing C header declarations, as cffi does.

Quick start

  1. 1

    Install pycparser with pip

    pip install pycparser
  2. 2

    Browse the examples directory for usage samples

Things to know

  • Most realistic C code needs an external C preprocessor (cpp, gcc -E or clang -E) before parsing.
  • The README does not say which standard headers are bundled in the pip package; the fake libc headers are not included in it.

Topics

#c-language#parser#ast#compiler-frontend#static-analysis#python#c99#c11

FAQ

What is pycparser?
A complete C99/C11 parser written in pure Python, producing an AST from C source code with no external dependencies. pycparser parses C source code and builds an abstract syntax tree (AST) that Python programs can traverse and modify. It follows the C grammar from Annex A of the C99 standard and aims to cover C11, with C23 support available through a dialect setting. It is implemented in pure Python with no dependencies beyond the interpreter, so it installs easily with pip.
Is pycparser free to use? What license does it have?
pycparser is open source under the Other license. Check the license terms before using it in commercial products.
Is pycparser still maintained?
Actively maintained. The last commit to pycparser was on Oct 19, 2026.
What can I use pycparser for?
Building a static code checker or linter for C code. Writing source-to-source transformations or obfuscators for C. Adding custom extensions to the C language through AST rewriting. Generating FFI bindings by parsing C header declarations, as cffi does.
How do I install pycparser?
Install pycparser with pip: pip install pycparser Browse the examples directory for usage samples
Where can I get pycparser?
The source code and installation instructions are on GitHub: https://github.com/eliben/pycparser

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