Use Rust module system.

[timkofu]

I have this package structure:

├── Cargo.toml
├── pyproject.toml
└── src
    ├── algorithm
    ├── lib.rs
    └── utility
        └── sum_as_string.rs

lib.rs has the following code:

use pyo3::prelude::{pymodule, Bound, PyModule, PyResult};
use pyo3::wrap_pyfunction;

mod utility {
    pub mod sum_as_string;
}

use utility::sum_as_string::sum_as_string;

#[pymodule]
fn iron(m: &Bound<'_, PyModule>) -> PyResult<()> {
    m.add_wrapped(wrap_pyfunction!(sum_as_string))?;
    Ok(())
}

And sum_as_string.rs has the following code:

use pyo3::prelude::{pyfunction, PyResult};

#[pyfunction]
pub fn sum_as_string(a: usize, b: usize) -> PyResult<String> {
    Ok((a + b).to_string())
}

That code emits the error:

error[E0425]: cannot find value `_PYO3_DEF` in module `wrapped_pyfunction`
  --> .../src/lib.rs:12:19
   |
12 |     m.add_wrapped(wrap_pyfunction!(sum_as_string))?;
   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not found in `wrapped_pyfunction`
   |
   = note: this error originates in the macro `wrap_pyfunction` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider importing one of these items
   |
1  + use crate::iron::_PYO3_DEF;
   |
1  + use crate::sum_as_string::sum_as_string::_PYO3_DEF;
   |

Neither of the two suggested uses in either file solves the problem; neither does use pyo3::prelude::*;.

How can update the code to use the imported function?

[timkofu]

Interesting. The modules need to be pure Rust, and PyO3 code be only in lib.rs. This is the code that has worked:

utility/sum_as_string.rs

pub fn sum_as_string(a: i8, b: i8) -> String {
    (a + b).to_string()
}

lib.rs

use pyo3::prelude::{pyfunction, pymodule, Bound, PyModule, PyResult};
use pyo3::wrap_pyfunction;

mod utility {
    pub mod sum_as_string;
}

use utility::sum_as_string::sum_as_string;

#[pyfunction]
fn sumasstring(a: i8, b: i8) -> PyResult<String> {
    Ok(sum_as_string(a, b))
}

#[pymodule]
fn iron(m: &Bound<'_, PyModule>) -> PyResult<()> {
    m.add_function(wrap_pyfunction!(sumasstring, m)?)?;
    Ok(())
}

Is this it, or is there a better way to do this?