How can I get a reference to a value in a Bound<PyDict>?

[rossmacarthur]

In an older version of pyo3 I had the following function

fn get_value_str<'a>(k: &str, dict: Option<&'a PyDict>) -> Option<&'a str> {
    dict
        .as_ref()
        .and_then(|d| d.get_item(k.to_lowercase()))
        .and_then(|v| v.extract::<&str>().ok())
}

Now I tried to do the following, but I get lifetime errors :(

fn get_value_str<'a>(k: &str, dict: Option<&Bound<'a, PyDict>>) -> Option<&'a str> {
    dict.and_then(|d| {
        d.get_item(k.to_lowercase())
            .ok()
            .flatten()
            .and_then(|v| v.extract::<&'a str>().ok())
    })
}

[davidhewitt]

I suggest one of the following solutions:

In PyO3 0.22 Bound<'py, PyString> now supports equality with &str. So depending on what you're trying to do, that might be enough:

fn get_value_str<'py>(k: &str, dict: Option<&Bound<'py, PyDict>>) -> Option<Bound<'py, PyString>> {
    dict?.get_item(k.to_lowercase()).ok()??.extract().ok()
}

Or you can use PyBackedStr if you want to store the result / drop the lifetime annotation:

fn get_value_str(k: &str, dict: Option<&Bound<'_, PyDict>>) -> Option<PyBackedStr> {
    dict?.get_item(k.to_lowercase()).ok()??.extract().ok()
}