Title

Creating a Lambda PyObject from Python Code in C-string

What will you learn?

In this tutorial, you will learn how to create a lambda PyObject from Python code stored in a C-string. This involves parsing the Python code string into an abstract syntax tree (AST) and converting it into a PyObject of type PyCodeObject, representing the function’s bytecode.

Introduction to the Problem and Solution

When working with the Python C API, there are situations where we need to create Python objects like functions using C code. If we have the Python code for a lambda function stored as a C string, we can convert it into a PyObject of type PyCodeObject, which represents the executable bytecode of the function. This allows seamless integration of Python functionality within our C program.

To achieve this, we first parse the Python code string into an abstract syntax tree (AST) using the compile function provided by the Python API. Subsequently, we transform this AST object into a PyCodeObject that encapsulates the executable bytecode of the lambda function.

Code

#include <Python.h>

int main() {
    // Define the Python code for Lambda Function as C String
    const char* python_code = "lambda x: x**2";

    // Compile the Python code string into an abstract syntax tree (AST)
    PyObject *ast = Py_CompileString(python_code, "", Py_file_input);

    // Convert AST to PyCodeObject representing executable bytecode
    PyObject *code = ((PyFunctionObject *) ast)->func_code;

    return 0;
}

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Explanation

• Define the lambda function’s Python code as a C string.
• Compile this string into an abstract syntax tree (PyObject) using Py_CompileString.
• Extract the PyCodeObject representing compiled bytecode by accessing ((PyFunctionObject *) ast)->func_code.
• Utilize this code object within your C program for executing or manipulating the defined lambda function.

How do I include necessary headers for using Python/C API?

Include <Python.h> at the beginning of your source file.

Can I directly execute this lambda function from my C program?

Yes, once converted to a PyCodeObject, you can call it using appropriate APIs provided by Python/C API.

What if my lambda function requires arguments or has multiple expressions?

Modify your approach accordingly while converting them into respective PyObjects.

Is it possible to define other types of functions similarly in C using Python’s AST?

Yes, follow similar steps for different types of functions or expressions defined in valid Python syntax.

How do I handle errors during compilation or conversion process?

Check error returns from functions like Py_CompileString and handle exceptions based on their documentation.

Can I embed additional logic around this generated lambda during runtime?

Yes, you can interact with and extend its behavior dynamically within your application logic written in C.

Conclusion

Creating a Lambda PyObject from its Python representation involves parsing Python strings and converting them into suitable C objects, enhancing flexibility in software development across both domains. This process facilitates seamless integration of Python functionality within native C applications, enabling powerful interactions between different programming paradigms.