Calling C/C++ from Python?

python

cross-platform

performance

best-practices

byAnton Shumikhin·Sep 16, 2024

To interface C/C++ in Python, ctypes, a built-in module in Python, is a great tool:

from ctypes import CDLL

# Load shared C library. Please replace 'mylib' with the name of your library
lib = CDLL('./mylib.so')

# Call a C function, say 'int add(int, int)', directly inside Python. Why do the math, when Python can do it for you?!
result = lib.add(3, 4)
print(result)  # Prints the absolute result of 3+4. Math is fun, right?

The Comprehensive Guide

How to Interface C/C++ functions

To activate C++ functions from Python:

Wrap your C++ code inside extern "C" to counteract C++ name-mangling. Because sometimes names can be deceiving!
Compile your code into a shared library. Libraries are more fun when they're shared, right?
Load and call the functions in Python using ctypes. It’s like making an international phone call.

Dealing with Data Structures

For complex data types and classes:

Boost.Python: Provides an elegant and seamless interface for Python to directly interact with C++. It's like a two-way dictionary!
pybind11: It's a light-weight library that provides bindings between modern C++ and Python. Less is more!
SWIG: It's a tool that helps you to convert nearly all constructs of C++ to Python.

Gotchas and Debugging Tips

While binding C++ libraries, don't forget:

All dependencies should be met. Sometimes, it's all about teamwork!
To install the python-dev package when SWIG is around. It's like SWIG's best friend.
Lastly, smack your library into a shared library suitable for your OS. Because one size definitely does NOT fit all!

Delving Deeper Into The Rabbit Hole

Thinking in terms of 'Speed'

Remember:

Update the C/C++ code for maximum efficiency.
It's wiser to avoid copying data between Python and C/C++ to minimize overhead.
Memory is a scarce resource. Use it wisely!

Getting the hang of pybind11 and Boost.Python

Here are some tips for using these tools:

You can test small changes using interactive Python sessions. No need for a full-fledged IDE!
Punch automation with tools like CMake. Time is of the essence!
Speed is nothing without control. Use Control C(++).