To call Python code in C, you must first initialize the interpreter, and then you can achieve interaction by executing strings, files, or calling specific functions. 1. Use Py_Initialize() to initialize the interpreter and close it with Py_Finalize(); 2. Use PyRun_SimpleString to execute string code or PyRun_SimpleFile to execute script files; 3. Import the module through PyImport_ImportModule, get the function through PyObject_GetAttrString, construct parameters of Py_BuildValue, call the function through PyObject_CallObject and process the return value; 4. Pay attention to version matching, path setting, reference count management and exception check. The entire process is structured clearly but requires careful handling of errors and resource management.

Calling Python code from C programs is not actually mysterious. The key is to use the C API provided by Python. As long as it is configured properly, you can create interpreters, execute scripts, and even pass parameters in C.

Initialize the Python interpreter

To call Python in C, the first step is to initialize the Python interpreter. This step is necessary, otherwise subsequent operations will fail.

• Use Py_Initialize() to start the interpreter
• Remember to call Py_Finalize() after use to free the resource
• If your program may be initialized and closed multiple times, you need to pay attention to thread safety issues (Python does not support multi-threaded embedding by default)

Sample code snippet:

 #include <Python.h>

int main() {
    Py_Initialize();
    // ... The code that calls Python Py_Finalize();
    return 0;
}

Note: You need to link Python libraries when compiling, such as using the -lpython3.10 parameter (the specific version depends on the Python version you installed).

Execute a simple Python script or statement

Once initialization is complete, you can directly run a piece of Python string code, such as printing a sentence or defining a function.

• Using PyRun_SimpleString is the easiest way
• It is suitable for executing some statements that do not require a return value

For example:

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

If you want to go a step further, such as executing a .py file, you can do this:

 FILE* fp = fopen("script.py", "r");
if (fp) {
    PyRun_SimpleFile(fp, "script.py");
    fclose(fp);
}

This method is suitable for situations when you want to load the entire script file, but be careful whether the path is correct and whether the file is readable.

Call Python function and get the return value

If you want to call a specific Python function and get its return value, you need a slightly more complicated operation.

The steps are as follows:

• Import module: Use PyImport_ImportModule
• Get function object: Use PyObject_GetAttrString
• Construct parameters: Create tuple or other types using Py_BuildValue
• Call function: Use PyObject_CallObject
• Process the return value: Check whether it is NULL, and then extract the actual value

For example, suppose there is a file called math_utils.py , with a function called add :

 # math_utils.py
def add(a, b):
    return ab

C calls it as follows:

 PyObject* pModule = PyImport_ImportModule("math_utils");
PyObject* pFunc = PyObject_GetAttrString(pModule, "add");

PyObject* pArgs = PyTuple_Pack(2, PyLong_FromLong(3), PyLong_FromLong(4));
PyObject* pResult = PyObject_CallObject(pFunc, pArgs);

long result = PyLong_AsLong(pResult);
// result == 7

This process is quite cumbersome, but the structure is clear. The key is to handle error checks at each step, such as determining whether pModule is NULL to avoid crashes.

Frequently Asked Questions and Precautions

• Python version matching : Make sure your C compile environment is linked to the correct Python version, otherwise compatibility issues may occur.
• Path settings : If the Python script is not in the current directory, you may need to set the search path through PySys_SetPath .
• Reference Count Management : Python uses the reference counting mechanism, remember to increase or decrease references appropriately to avoid memory leaks.
• Exception handling : It is best to check whether any exceptions occur after each call to the Python API. You can use PyErr_Occurred() to judge.

Basically that's it. Although it seems a bit troublesome, as long as you follow the process step by step, you can successfully implement the function of C calling Python.

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