Taking a tuple (&str, &str) as an argument

[dralley]

I have some code that used to work on an older version of PyO3 (0.20.0)

        #[setter(checksum)]
        pub fn set_checksum(&mut self, checksum: (&str, &str)) -> PyResult<()> {
            let checksum = crate::metadata::Checksum::try_create(checksum.0, checksum.1)?;
            self.inner.set_checksum(checksum);
            Ok(())
        }

This code now raises the error:

the trait bound `(&str, &str): PyFunctionArgument<'_, '_, false>` is not satisfied
the following other types implement trait `FromPyObject<'py>`:
  (T0, T1)
  (T0, T1, T2)
  (T0, T1, T2, T3)
  (T0, T1, T2, T3, T4)
  (T0, T1, T2, T3, T4, T5)
  (T0, T1, T2, T3, T4, T5, T6)
  (T0, T1, T2, T3, T4, T5, T6, T7)
  (T0, T1, T2, T3, T4, T5, T6, T7, T8)
and 4 others
required for `(&str, &str)` to implement `FromPyObjectBound<'_, '_>`
required for `(&str, &str)` to implement `PyFunctionArgument<'_, '_, false>`rustc[Click for full compiler diagnostic](rust-analyzer-diagnostics-view:/diagnostic%20message%20[0]?0#file:///home/dralley/Devel/rpm-dev/rpmrepo_metadata/src/python_ext.rs)
extract_argument.rs(119, 8): required by a bound in `extract_argument`

What is the most idiomatic and proper way to write this code now?

P.S. More "real" examples that go beyond passing simple strings or integers would be greatly appreciated. I've done lots of searching and haven't seen much of anything that looks like this.

[mejrs]

Can you provide the full diagnostic?

[dralley]

dralley@fedora:~/Devel/rpm-dev/rpmrepo_metadata$ maturin build
📦 Including license file "/home/dralley/Devel/rpm-dev/rpmrepo_metadata/LICENSE.txt"
🔗 Found pyo3 bindings
🐍 Found CPython 3.13 at /usr/bin/python3
warning: unused manifest key: profile.release.debuginfo
   Compiling pyo3-build-config v0.24.2
   Compiling pyo3-ffi v0.24.2
   Compiling pyo3-macros-backend v0.24.2
   Compiling pyo3 v0.24.2
   Compiling pyo3-macros v0.24.2
   Compiling rpmrepo_metadata v0.3.0 (/home/dralley/Devel/rpm-dev/rpmrepo_metadata)
warning: elided lifetime has a name
   --> src/metadata.rs:725:47
    |
725 |     pub fn to_values<'a>(&'a self) -> Result<(&str, &'a str), MetadataError> {
    |                      --                       ^ this elided lifetime gets resolved as `'a`
    |                      |
    |                      lifetime `'a` declared here
    |
    = note: `#[warn(elided_named_lifetimes)]` on by default

error[E0277]: the trait bound `(&str, &str): PyFunctionArgument<'_, '_, false>` is not satisfied
   --> src/python_ext.rs:210:50
    |
210 |         pub fn set_checksum(&mut self, checksum: (&str, &str)) -> PyResult<()> {
    |                                                  ^^^^^^^^^^^^ the trait `FromPyObject<'_>` is not implemented for `(&str, &str)`
    |
    = help: the following other types implement trait `FromPyObject<'py>`:
              (T0, T1)
              (T0, T1, T2)
              (T0, T1, T2, T3)
              (T0, T1, T2, T3, T4)
              (T0, T1, T2, T3, T4, T5)
              (T0, T1, T2, T3, T4, T5, T6)
              (T0, T1, T2, T3, T4, T5, T6, T7)
              (T0, T1, T2, T3, T4, T5, T6, T7, T8)
            and 4 others
    = note: required for `(&str, &str)` to implement `FromPyObjectBound<'_, '_>`
    = note: required for `(&str, &str)` to implement `PyFunctionArgument<'_, '_, false>`
note: required by a bound in `extract_argument`
   --> /home/dralley/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/pyo3-0.24.2/src/impl_/extract_argument.rs:119:8
    |
113 | pub fn extract_argument<'a, 'py, T, const IS_OPTION: bool>(
    |        ---------------- required by a bound in this function
...
119 |     T: PyFunctionArgument<'a, 'py, IS_OPTION>,
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `extract_argument`

warning: unused variable: `hash`
   --> src/metadata.rs:626:27
    |
626 |             Self::Unknown(hash) => unimplemented!(),
    |                           ^^^^ help: if this is intentional, prefix it with an underscore: `_hash`
    |
    = note: `#[warn(unused_variables)]` on by default

warning: unused variable: `updateinfo_path`
   --> src/repository.rs:330:18
    |
330 |             let (updateinfo_path, updateinfo_writer) = utils::xml_writer_for_path(
    |                  ^^^^^^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_updateinfo_path`

For more information about this error, try `rustc --explain E0277`.
warning: `rpmrepo_metadata` (lib) generated 3 warnings
error: could not compile `rpmrepo_metadata` (lib) due to 1 previous error; 3 warnings emitted
💥 maturin failed
  Caused by: Failed to build a native library through cargo
  Caused by: Cargo build finished with "exit status: 101": `env -u CARGO PYO3_ENVIRONMENT_SIGNATURE="cpython-3.13-64bit" PYO3_PYTHON="/usr/bin/python3" PYTHON_SYS_EXECUTABLE="/usr/bin/python3" "cargo" "rustc" "--message-format" "json-render-diagnostics" "--manifest-path" "/home/dralley/Devel/rpm-dev/rpmrepo_metadata/Cargo.toml" "--lib" "--crate-type" "cdylib"`

[mejrs]

Anyway, this is probably because you're using an older Python version. When we migrated to the Bound api we had to gate FromPyObjectBound for &str behind #[cfg(any(Py_3_10, not(Py_LIMITED_API)))]. If you can't get around that, use https://docs.rs/pyo3/latest/pyo3/pybacked/struct.PyBackedStr.html instead.

[dralley]

Python 3.13

[Icxolu]

Due to the FromPyObject/FromPyObjectBound split we currently still have, borrowing does not work inside of tuples, only directly in argument position (#4390 should solve that). If you can live with a copy (String, String) should also work.

[alex]

https://docs.rs/pyo3/latest/pyo3/pybacked/struct.PyBackedStr.html is another option

…

On Sun, Apr 27, 2025 at 3:22 PM Icxolu ***@***.***> wrote: Due to the FromPyObject/FromPyObjectBound split we currently still have, borrowing does not work inside of tuples, only directly in argument position (#4390 should solve that). If you can live with a copy (String, String) should also work. — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

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