pyo3/pytests/src/dict_iter.rs

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

#[pymodule]
pub fn dict_iter(m: &Bound<'_, PyModule>) -> PyResult<()> {
    m.add_class::<DictSize>()?;
    Ok(())
}

#[pyclass]
pub struct DictSize {
    expected: u32,
}

#[pymethods]
impl DictSize {
    #[new]
    fn new(expected: u32) -> Self {
        DictSize { expected }
    }

    fn iter_dict(&mut self, _py: Python<'_>, dict: &Bound<'_, PyDict>) -> PyResult<u32> {
        let mut seen = 0u32;
        for (sym, values) in dict {
            seen += 1;
            println!(
                "{:4}/{:4} iterations:{}=>{}",
                seen, self.expected, sym, values
            );
        }

        if seen == self.expected {
            Ok(seen)
        } else {
            Err(PyErr::new::<PyRuntimeError, _>(format!(
                "Expected {} iterations - performed {}",
                self.expected, seen
            )))
        }
    }
}