Destructure arguments in function signatures

[nickdrozd]

I would like to destructure compound types in function signatures:

type CompoundType = (u64, u64);

#[pyfunction]
pub fn function((arg1, arg2): CompoundType) {}

But this is currently not supported:

error: destructuring in arguments is not supported
  --> src/lib.rs:39:17
   |
39 | pub fn function((arg1, arg2): CompoundType) {}
   |                 ^^^^^^^^^^^^

[davidhewitt]

While I'm open to this in principle, what would the argument be called on the Python side? At the moment we use the single identifier of the variable as the python argument name.

We could require something like a #[pyo3(name = "foo")] annotation on this pattern argument, I guess. I've wanted the ability to change the Python name of arguments in the past e.g. for unused arguments:

#[pyfunction]
fn bar(#[pyo3(name = "foo")] _foo: Foo) {
   // _foo is never used
}

So maybe with the requirement of needing a Python name annotation, this would be possible. Other opinions welcome!

[alex]

It's worth noting that Python used to support unpacking tuples in function signatures, and it was removed in Python 3. From that perspective I think it may add more confusion?

On Mon, Jun 3, 2024 at 1:40 PM David Hewitt @.***> wrote:

While I'm open to this in principle, what would the argument be called on the Python side? At the moment we use the single identifier of the variable as the python argument name.

We could require something like a #[pyo3(name = "foo")] annotation on this pattern argument, I guess. I've wanted the ability to change the Python name of arguments in the past e.g. for unused arguments:

[pyfunction]fn bar(#[pyo3(name = "foo")] _foo: Foo) {

// _foo is never used}

So maybe with the requirement of needing a Python name annotation, this would be possible. Other opinions welcome!

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[davidhewitt]

That's a very good point. It's also quite easy to just move the destructuring into the first line of the function, so it's not like this requires a difficult workaround...

[mejrs]

I've wanted this to make it easier to work with newtypes but also ran into "then what do we get argument names from" problem. I would prefer an additional line inside the function over something like #[pyo3(name = "foo")]. I'm really not a fan of those.