Passing variables to an embedded Python script from C++

Question

I need to run a Python script from c++, but I need also to pass it some variables. It can't be a function with parameters, because there are hundreds of variables, so the syntax would become too messy. I will post a simple example, analogue to my case. This is the Python script:

script.py

c = 10 * 5 + a
print(c)

And this is the calling code:

#include "Python.h"

int main()
{
    Py_Initialize();
    
    PyObject *pName = PyUnicode_FromString("script");
    PyObject *pModule = PyImport_Import(pName);;
    
    // Add something to set the cariable "a" in the script
    
    Py_Finalize();
}

Could you help with the code to add to set the variable "a" in the script?

Does this answer your question? Embedding python in C++: Assigning C++ and python variables — mugiseyebrows
– mugiseyebrows, Commented Oct 7, 2022 at 13:12
Hi @mugiseyebrows, this answer is doing the opposite: it is assigning to a c++ variable the value of a variable in the Python script. Instead I need to assign the value of a c++ variable to the script, before it is executed. — Mattia
– Mattia, Commented Oct 7, 2022 at 14:26
If the contents of your script are as you say, then wouldn't the code already be executed at import time? I think you want PyRun_FileExFlags instead with a custom globals dictionary. — Botje
– Botje, Commented Oct 7, 2022 at 14:43
@Botje, I think your comment makes sense. Can you help with the example code so I can test it? — Mattia
– Mattia, Commented Oct 7, 2022 at 15:02

Botje · Accepted Answer · 2022-10-07 15:47:20Z

2

The following will do the trick:

Py_Initialize();
    
PyObject *locals = PyDict_New();
PyObject *globals = PyDict_New();

PyDict_SetItemString(locals, "a", PyLong_FromLong(123));
PyDict_SetItemString(locals, "b", PyLong_FromLong(9));

PyRun_FileExFlags(fopen("script.py", "r"), "script.py", Py_file_input, globals, locals, 1, NULL);

Py_Finalize();

answered Oct 7, 2022 at 15:47

Botje

32.1k4 gold badges36 silver badges47 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Mattia Over a year ago

Thanks @Botje, your solution is working, I added this line PyObject* val = PyDict_GetItemString(locals, "c"); and val has the correct value. The only unexpected issue is that the console is not printing the value of c as from the command in the last line of the Python script. Is it possible to get that output in the console?

Botje Over a year ago

The print shows up for me...

Collectives™ on Stack Overflow

Passing variables to an embedded Python script from C++

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related