pyo3/types/
traceback.rs

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use crate::err::{error_on_minusone, PyResult};
use crate::types::{any::PyAnyMethods, string::PyStringMethods, PyString};
use crate::{ffi, Bound, PyAny};

/// Represents a Python traceback.
///
/// Values of this type are accessed via PyO3's smart pointers, e.g. as
/// [`Py<PyTraceback>`][crate::Py] or [`Bound<'py, PyTraceback>`][Bound].
///
/// For APIs available on traceback objects, see the [`PyTracebackMethods`] trait which is implemented for
/// [`Bound<'py, PyTraceback>`][Bound].
#[repr(transparent)]
pub struct PyTraceback(PyAny);

pyobject_native_type_core!(
    PyTraceback,
    pyobject_native_static_type_object!(ffi::PyTraceBack_Type),
    #checkfunction=ffi::PyTraceBack_Check
);

/// Implementation of functionality for [`PyTraceback`].
///
/// These methods are defined for the `Bound<'py, PyTraceback>` smart pointer, so to use method call
/// syntax these methods are separated into a trait, because stable Rust does not yet support
/// `arbitrary_self_types`.
#[doc(alias = "PyTraceback")]
pub trait PyTracebackMethods<'py>: crate::sealed::Sealed {
    /// Formats the traceback as a string.
    ///
    /// This does not include the exception type and value. The exception type and value can be
    /// formatted using the `Display` implementation for `PyErr`.
    ///
    /// # Example
    ///
    /// The following code formats a Python traceback and exception pair from Rust:
    ///
    /// ```rust
    /// # use pyo3::{Python, PyResult, prelude::PyTracebackMethods, ffi::c_str};
    /// # let result: PyResult<()> =
    /// Python::with_gil(|py| {
    ///     let err = py
    ///         .run(c_str!("raise Exception('banana')"), None, None)
    ///         .expect_err("raise will create a Python error");
    ///
    ///     let traceback = err.traceback(py).expect("raised exception will have a traceback");
    ///     assert_eq!(
    ///         format!("{}{}", traceback.format()?, err),
    ///         "\
    /// Traceback (most recent call last):
    ///   File \"<string>\", line 1, in <module>
    /// Exception: banana\
    /// "
    ///     );
    ///     Ok(())
    /// })
    /// # ;
    /// # result.expect("example failed");
    /// ```
    fn format(&self) -> PyResult<String>;
}

impl<'py> PyTracebackMethods<'py> for Bound<'py, PyTraceback> {
    fn format(&self) -> PyResult<String> {
        let py = self.py();
        let string_io = py
            .import(intern!(py, "io"))?
            .getattr(intern!(py, "StringIO"))?
            .call0()?;
        let result = unsafe { ffi::PyTraceBack_Print(self.as_ptr(), string_io.as_ptr()) };
        error_on_minusone(py, result)?;
        let formatted = string_io
            .getattr(intern!(py, "getvalue"))?
            .call0()?
            .downcast::<PyString>()?
            .to_cow()?
            .into_owned();
        Ok(formatted)
    }
}

#[cfg(test)]
mod tests {
    use crate::IntoPyObject;
    use crate::{
        ffi,
        types::{any::PyAnyMethods, dict::PyDictMethods, traceback::PyTracebackMethods, PyDict},
        PyErr, Python,
    };

    #[test]
    fn format_traceback() {
        Python::with_gil(|py| {
            let err = py
                .run(ffi::c_str!("raise Exception('banana')"), None, None)
                .expect_err("raising should have given us an error");

            assert_eq!(
                err.traceback(py).unwrap().format().unwrap(),
                "Traceback (most recent call last):\n  File \"<string>\", line 1, in <module>\n"
            );
        })
    }

    #[test]
    fn test_err_from_value() {
        Python::with_gil(|py| {
            let locals = PyDict::new(py);
            // Produce an error from python so that it has a traceback
            py.run(
                ffi::c_str!(
                    r"
try:
    raise ValueError('raised exception')
except Exception as e:
    err = e
"
                ),
                None,
                Some(&locals),
            )
            .unwrap();
            let err = PyErr::from_value(locals.get_item("err").unwrap().unwrap());
            let traceback = err.value(py).getattr("__traceback__").unwrap();
            assert!(err.traceback(py).unwrap().is(&traceback));
        })
    }

    #[test]
    fn test_err_into_py() {
        Python::with_gil(|py| {
            let locals = PyDict::new(py);
            // Produce an error from python so that it has a traceback
            py.run(
                ffi::c_str!(
                    r"
def f():
    raise ValueError('raised exception')
"
                ),
                None,
                Some(&locals),
            )
            .unwrap();
            let f = locals.get_item("f").unwrap().unwrap();
            let err = f.call0().unwrap_err();
            let traceback = err.traceback(py).unwrap();
            let err_object = err.clone_ref(py).into_pyobject(py).unwrap();

            assert!(err_object.getattr("__traceback__").unwrap().is(&traceback));
        })
    }
}