How to accept a Python string or Python None in a function

[hwittenborn]

I've got a function that accepts two strings, but I'm wanting them to also be able to be set to None. Originally I thought of using this:

fn my_function(arg1: Option<String>, arg2: Option<String>) {

But this seems to make the arguments able to be omitted. I don't want the arguments to be able to be omitted though, I just want them to be nullable with None.

Is there any way to do what I'm wanting?

[adamreichold]

Try adding a signature indicating that the arguments are mandatory and do not have a default value, e.g.

#[pyfunction]
#[pyo3(signature=(arg1, arg2))]
fn my_function(arg1: Option<String>, arg2: Option<String>) {

[hwittenborn]

That doesn't seem to be working, I'm thinking it might be the context I'm using it in, I'm using it in a class constructor like so:

#[pyclass]
pub struct DistroArchPair {
    pub distro: Option<String>,
    pub arch: Option<String>
}

#[pymethods]
impl DistroArchPair {
    #[new]
    fn new(distro: Option<String>, arch: Option<String>) -> Self {
        Self {
            distro,
            arch
        }
    }
}

Adding #[pyo3(signature=(arg1, arg2))] below #[new] prints the following compiler error:

error: expected literal
  --> src/python.rs:25:22
   |
25 |     #[pyo3(signature=(arg1, arg2))]
   |                      ^

Sorry for being vague about it before, I just didn't want to send anything that complicated, but then I checked my code again and realized the affected part is quite tiny.

[birkenfeld]

Are you using PyO3 0.18 or earlier? This syntax is new in this version.

[adamreichold]

I will check, but I think for #[new] the signature must be put on the #[pyclass] instead?

[adamreichold]

Ah sorry, that was text_signature, signature should work, c.f. #2866 and https://pyo3.rs/v0.18.0/class#method-arguments

[hwittenborn]

Are you using PyO3 0.18 or earlier? This syntax is new in this version.

That was it, everything worked fine after upgrading my version. Thanks a ton!

[hwittenborn]

Oh, thanks for the really quick support from all of you too! It's really helping me to get everything I need done :)

[davidhewitt]

For what it's worth, I'm adding a little bit of documentation for this case in #2934