How to Call a Python Script from C++

Integrating Python scripts into a C++ application can be incredibly useful, especially when leveraging Python's rich ecosystem of libraries for data science, machine learning, or automation. In this guide, we'll explore the most popular and efficient way to call Python code from C++ using the Python.h header provided by the Python C API.

Prerequisites

Before proceeding, ensure you have the following installed:

Python (preferably Python 3.x)
A C++ compiler (like GCC or MSVC)
Python development headers (Python.h)

On Linux, install Python headers using:

sudo apt-get install python3-dev

On Windows, ensure Python is added to your system PATH.

Using the Python C API

The Python C API allows seamless interaction between C/C++ and Python. Here's a step-by-step guide:

Step 1: Include Python Headers

In your C++ file, include the Python header:

#include <Python.h>

Step 2: Initialize the Python Interpreter

Before calling any Python code, initialise the interpreter:

Py_Initialize();

Step 3: Run a Python Script

Use PyRun_SimpleString to execute Python code directly:

PyRun_SimpleString("print('Hello from Python!')");

Alternatively, run a Python script from a file:

FILE* file = fopen("script.py", "r");
PyRun_SimpleFile(file, "script.py");
fclose(file);

Step 4: Finalise the Interpreter

Clean up resources when done:

Py_Finalize();

Compiling the C++ Program

When compiling, link against the Python library. For example, on Linux:

g++ -o my_program my_program.cpp -I/usr/include/python3.8 -lpython3.8

On Windows, ensure the Python include and library paths are correctly set in your compiler.

Alternative: Using Boost.Python

For a more C++-friendly approach, consider Boost.Python. It simplifies embedding Python in C++ but requires additional setup.

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