Can't use rust keywords as python function names

[Databean]

Bug Description

Using a rust keyword as the name of a function, e.g. #[pyo3(name = "<struct>")] results in a compilation error.

Steps to Reproduce

Sample program:

use pyo3::prelude::*;

#[pyclass(frozen, subclass)]
struct MyClass {
}

#[pymethods]
impl MyClass {
    #[new]
    fn new() -> Self {
        MyClass {}
    }

    #[pyo3(name = "struct")]
    fn struct_method(&self) -> usize {
        42
    }
}

#[pyfunction]
#[pyo3(name = "struct")]
fn struct_function() -> usize {
    42
}

/// A Python module implemented in Rust.
#[pymodule]
fn pyo3_example(_py: Python, m: &Bound<PyModule>) -> PyResult<()> {
    m.add_class::<MyClass>()?;
    m.add_function(wrap_pyfunction!(struct_function, m)?)?;
    Ok(())
}

Backtrace

$ RUSTFLAGS="-Zmacro-backtrace" cargo build
   Compiling pyo3_example v0.1.0 (/home/data/programming/pyo3_example)
error: expected a single identifier in double quotes
  --> src/lib.rs:14:19
   |
14 |     #[pyo3(name = "struct")]
   |                   ^^^^^^^^

error: expected a single identifier in double quotes
  --> src/lib.rs:21:15
   |
21 | #[pyo3(name = "struct")]
   |               ^^^^^^^^

error[E0433]: failed to resolve: function `wrapped_pyfunction` is not a crate or module
   --> /home/data/.cargo/registry/src/index.crates.io-6f17d22bba15001f/pyo3-0.21.2/src/macros.rs:153:14
    |
135 | macro_rules! wrap_pyfunction {
    | ---------------------------- in this expansion of `wrap_pyfunction!`
...
153 |             &wrapped_pyfunction::_PYO3_DEF,
    |              ^^^^^^^^^^^^^^^^^^ function `wrapped_pyfunction` is not a crate or module
    |
   ::: src/lib.rs:30:20
    |
30  |     m.add_function(wrap_pyfunction!(struct_function, m)?)?;
    |                    ------------------------------------ in this macro invocation

For more information about this error, try `rustc --explain E0433`.
error: could not compile `pyo3_example` (lib) due to 3 previous errors

Your operating system and version

$ uname -a
Linux data-desktop 6.9.1-arch1-2 #1 SMP PREEMPT_DYNAMIC Wed, 22 May 2024 13:47:07 +0000 x86_64 GNU/Linux

Your Python version (python --version)

Python 3.12.3

Your Rust version (rustc --version)

rustc 1.80.0-nightly (867900499 2024-05-23)

Your PyO3 version

0.21.2

How did you install python? Did you use a virtualenv?

$ pacman -S pyton
$ python3 -m venv .venv
$ source .venv/bin/activate
$ cargo build

Additional Info

struct is not a reserved word in Python, so it works normally as Python code:

class MyClass:
    def struct(self):
        return 42

def struct():
    return 42

m = MyClass()
print(m.struct())
print(struct())

[Databean]

Created #4226 to fix this issue.

[Icxolu]

This is also already possibly by using a raw identifier:

#[pyo3(name = "r#struct")]
fn struct_method(&self) -> usize {
    42
}

[Databean]

This is also already possibly by using a raw identifier:

#[pyo3(name = "r#struct")]
fn struct_method(&self) -> usize {
    42
}

This does work for the method, thanks:

>> import pyo3_example
>> m = pyo3_example.MyClass()
>> m.struct()
42

But it does not work for the standalone function:

>> import pyo3_example
>> pyo3_example.struct()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: module 'pyo3_example' has no attribute 'struct'. Did you mean: 'r#struct'?
>> pyo3_example.r#struct
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: module 'pyo3_example' has no attribute 'r'
>> pyo3_example["r#struct"]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'module' object is not subscriptable

#[pyo3(name = r#struct)] doesn't work either, still giving

error: expected string literal
--> src/lib.rs:21:15
|
21 | #[pyo3(name = r#struct)]
|               ^^^^^^^^

[Icxolu]

It does work for standalone functions, if you use the raw identifier for the function itself:

#[pyfunction]
fn r#struct() -> usize {
    42
}

The syntax for the pyo3 attribute is (notice the quotes):

#[pyfunction]
#[pyo3(name = "r#struct")]
fn some_function -> usize {
    42
}

But this currently does also not work, but I would consider that a bug (I did track that down already, so fixing that should be easy).

[davidhewitt]

I'd hope that name = "r#struct" shouldn't be necessary, as I mostly view the r# bit as a syntax ugly that's necessary to escape the parser handling keywords when not wanted. So my personal take is that I'd probably prefer

#[pyfunction]
#[pyo3(name = "r#struct")]
fn some_function -> usize {
    42
}

to continue to be invalid.

[Icxolu]

Just for reference, your example is not invalid (in the sense that is does compile just fine), it just produces no usable function on the Python side.

[davidhewitt]

😬