exec() Python code in Rust, have results in the

[nschloe]

In Rust, I have a piece of Python code. I'd like to exec it such that it's results are present in the default globals() namespace, i.e., when calling foo() from Python in the following example, the variable a should be present and have the value 1.

use pyo3::prelude::*;
use pyo3::types::PyDict;

#[pyfunction]
fn foo() -> PyResult<()> {
    let code = CString::new("a = 1").unwrap();

    Python::with_gil(|py| {
        let locals = PyDict::new(py);
        py.run(&code, Some(&locals), Some(&locals))?;
        Ok(())
    })
}

The culprit seems to be the PyDict. Any hint on what I should do instead?
Perhaps py.run isn't the correct function to use here?

[birkenfeld]

That's not something that could or should work. To put it into perspective, you couldn't write a foo() function in a separate module in pure Python either that can modify the globals of the calling module. Well, it being Python, you can, but it's ugly and not at all recommended.

[nschloe]

Thanks for your response! I see your point, but in my experience, this kind of functionality has been useful. With nanobind (and previously pybind11), I’ve used something like:

auto const code = "a = 1";
auto scope = nb::globals();
nb::exec(nb::str(code), scope);

which, if I understand correctly, ultimately relies on PyEval_GetGlobals() and PyEval_EvalCode(codeobj.ptr(), global.ptr(), local.ptr()). This approach has worked well for me in the past.

Could you clarify why this would be problematic in PyO3? Is it a limitation of how PyO3 interacts with Python’s execution model, or is there another approach you’d recommend for achieving the same effect? I’d really appreciate any insights!

[nschloe]

I think I can just fill a dictionary in rust, return it, and .update() globals() in Python.

[birkenfeld]

But globals() or PyEval_GetGlobals() also just get you the module globals.

Have you tried setting the globals and locals arguments to None?