autopxd2

Automatically generate Cython .pxd declaration files from C/C++ header files.

Overview

autopxd2 parses C header files and generates Cython .pxd files, enabling you to call C libraries from Cython without manually writing declarations.

Key features:

• Generates complete .pxd files from C/C++ headers
• Full C++ support with libclang backend
• Automatic system include path detection
• Auto-generates cimport statements for standard library types
• Cross-platform support (Linux, macOS, Windows)

Supported Features

C Features

Feature	libclang	pycparser (legacy)
Structs and unions	✓	✓
Enums (with expressions)	✓	✓
Typedefs	✓	✓
Function declarations	✓	✓
Function pointers	✓	✓
Arrays (fixed and flexible)	✓	✓
Pointers and const qualifiers	✓	✓
Forward declarations	✓	✓
Anonymous structs/unions	✓	✓
Bit fields	✓	✓
#define macros (int, float, string)	✓
Circular type dependencies	✓

C++ Features (libclang only)

Feature	Supported
Classes with fields and methods	✓
Namespaces (including nested)	✓
Templates with type parameters	✓
Template specializations	✓
Operator overloading (renamed for Cython)	✓
References and const references	✓
Inheritance declarations	✓
Static methods and fields	✓

Installation

pip install autopxd2

Recommended: Install the libclang backend for full C/C++ support. The clang2 package version must match your system's LLVM version:

# One-liner: detect LLVM version and install matching clang2
pip install "clang2==$(llvm-config --version | cut -d. -f1).*"

# Or check version manually first
llvm-config --version  # e.g., 18.1.3 means you need clang2==18.*
pip install "clang2==18.*"

Without clang2, autopxd2 falls back to the legacy pycparser backend (C99 only, no macros, no circular dependency handling). If clang2 is missing, autopxd2 will detect your LLVM version and show the exact install command.

See the installation docs for platform-specific LLVM setup (macOS with Homebrew, Ubuntu/Debian, Windows).

Quick Start

# Generate a .pxd file from a C header
autopxd myheader.h myheader.pxd

# Add project-specific include directories (system includes are auto-detected)
autopxd -I ./include myheader.h myheader.pxd

# Write to stdout (omit output file)
autopxd myheader.h > myheader.pxd

Usage

autopxd [OPTIONS] INFILE [OUTFILE]

Options marked [libclang] require the libclang backend.

Options:
  -v, --version              Print version and exit.
  -b, --backend <name>       Parser backend (default: auto, prefers libclang).
  --list-backends            List available backends and exit.
  -q, --quiet                Suppress warnings.
  --debug / --no-debug       Print debug info to stderr.
  -I, --include-dir <dir>    Add include search path.
  -D, --define <macro>       Define preprocessor macro.
  -w, --whitelist <pattern>  Only emit from files matching pattern.
  -x, --cpp                  [libclang] Parse as C++.
  --std <std>                [libclang] Language standard (e.g., c11, c++17).
  --clang-arg <arg>          [libclang] Pass argument to clang.
  --no-default-includes      [libclang] Disable system include auto-detection.
  -p, --project-prefix       [libclang] Whitelist paths for umbrella headers.
  --no-recursive             [libclang] Disable recursive include parsing.
  --max-depth <n>            [libclang] Max depth for recursive includes.
  -h, --help                 Show this message and exit.

Automatic Imports

autopxd2 automatically generates cimport statements for commonly used types when using the libclang backend.

Cython Standard Library Types

When headers use types from C standard library headers, autopxd generates appropriate Cython cimports:

// input.h
#include <stdio.h>
#include <stdint.h>

uint32_t process(FILE *f);

# Generated output
from libc.stdint cimport uint32_t
from libc.stdio cimport FILE

cdef extern from "input.h":
    uint32_t process(FILE* f)

Bundled Stub Types

For types not in Cython's standard library, autopxd provides bundled stub declarations:

// input.h
#include <stdarg.h>

void log_message(const char *fmt, va_list args);

# Generated output
from autopxd.stubs.stdarg cimport va_list

cdef extern from "input.h":
    void log_message(const char* fmt, va_list args)

C++ STL Types

C++ standard library types are automatically imported from libcpp:

// input.hpp
#include <vector>
#include <string>

std::vector<std::string> get_items();

# Generated output
from libcpp.string cimport string
from libcpp.vector cimport vector

cdef extern from "input.hpp":
    vector[string] get_items()

Note: Auto-import requires the libclang backend for header detection. The pycparser backend does not track included headers.

Documentation

Full documentation is available at elijahr.github.io/python-autopxd2.

Docker

A Docker image with libclang pre-installed is available:

docker run --rm -v $(pwd):/work -w /work ghcr.io/elijahr/python-autopxd2 autopxd myheader.h

See Docker Usage for more examples.

Contributing

Contributions are welcome. See CONTRIBUTING.md for development setup and guidelines.

License

MIT License. See LICENSE for details.

Acknowledgments

This project is a fork of python-autopxd by Thiago de Arruda.