Struct PyErr

pub struct PyErr { /* private fields */ }

Available on crate features dep_pyo3 and std only.

Represents a Python exception.

To avoid needing access to Python in Into conversions to create PyErr (thus improving compatibility with ? and other Rust errors) this type supports creating exceptions instances in a lazy fashion, where the full Python object for the exception is created only when needed.

Accessing the contained exception in any way, such as with value_bound, get_type_bound, or is_instance_bound will create the full exception object if it was not already created.

Implementations

impl PyErr

pub fn new<T, A>(args: A) -> PyErr

where T: PyTypeInfo, A: PyErrArguments + Send + Sync + 'static,

Creates a new PyErr of type T.

args can be:

• a tuple: the exception instance will be created using the equivalent to the Python expression T(*tuple)
• any other value: the exception instance will be created using the equivalent to the Python expression T(value)

This exception instance will be initialized lazily. This avoids the need for the Python GIL to be held, but requires args to be Send and Sync. If args is not Send or Sync, consider using PyErr::from_value_bound instead.

If T does not inherit from BaseException, then a TypeError will be returned.

If calling T’s constructor with args raises an exception, that exception will be returned.

Examples

use pyo3::prelude::*;
use pyo3::exceptions::PyTypeError;

#[pyfunction]
fn always_throws() -> PyResult<()> {
    Err(PyErr::new::<PyTypeError, _>("Error message"))
}

In most cases, you can use a concrete exception’s constructor instead:

use pyo3::prelude::*;
use pyo3::exceptions::PyTypeError;

#[pyfunction]
fn always_throws() -> PyResult<()> {
    Err(PyTypeError::new_err("Error message"))
}

pub fn from_type<A>(ty: Bound<'_, PyType>, args: A) -> PyErr

where A: PyErrArguments + Send + Sync + 'static,

Constructs a new PyErr from the given Python type and arguments.

ty is the exception type; usually one of the standard exceptions like exceptions::PyRuntimeError.

args is either a tuple or a single value, with the same meaning as in PyErr::new.

If ty does not inherit from BaseException, then a TypeError will be returned.

If calling ty with args raises an exception, that exception will be returned.

pub fn from_type_bound<A>(ty: Bound<'_, PyType>, args: A) -> PyErr

where A: PyErrArguments + Send + Sync + 'static,

👎Deprecated since 0.23.0: renamed to PyErr::from_type

Deprecated name for PyErr::from_type.

pub fn from_value(obj: Bound<'_, PyAny>) -> PyErr

Creates a new PyErr.

If obj is a Python exception object, the PyErr will contain that object.

If obj is a Python exception type object, this is equivalent to PyErr::from_type(obj, ()).

Otherwise, a TypeError is created.

Examples

use pyo3::prelude::*;
use pyo3::PyTypeInfo;
use pyo3::exceptions::PyTypeError;
use pyo3::types::PyString;

Python::with_gil(|py| {
    // Case #1: Exception object
    let err = PyErr::from_value(PyTypeError::new_err("some type error")
        .value(py).clone().into_any());
    assert_eq!(err.to_string(), "TypeError: some type error");

    // Case #2: Exception type
    let err = PyErr::from_value(PyTypeError::type_object(py).into_any());
    assert_eq!(err.to_string(), "TypeError: ");

    // Case #3: Invalid exception value
    let err = PyErr::from_value(PyString::new(py, "foo").into_any());
    assert_eq!(
        err.to_string(),
        "TypeError: exceptions must derive from BaseException"
    );
});

pub fn from_value_bound(obj: Bound<'_, PyAny>) -> PyErr

👎Deprecated since 0.23.0: renamed to PyErr::from_value

Deprecated name for PyErr::from_value.

pub fn get_type<'py>(&self, py: Python<'py>) -> Bound<'py, PyType>

Returns the type of this exception.

Examples

use pyo3::{prelude::*, exceptions::PyTypeError, types::PyType};

Python::with_gil(|py| {
    let err: PyErr = PyTypeError::new_err(("some type error",));
    assert!(err.get_type(py).is(&PyType::new::<PyTypeError>(py)));
});

pub fn get_type_bound<'py>(&self, py: Python<'py>) -> Bound<'py, PyType>

👎Deprecated since 0.23.0: renamed to PyErr::get_type

Deprecated name for PyErr::get_type.

pub fn value<'py>(&self, py: Python<'py>) -> &Bound<'py, PyBaseException>

Returns the value of this exception.

Examples

use pyo3::{exceptions::PyTypeError, PyErr, Python};

Python::with_gil(|py| {
    let err: PyErr = PyTypeError::new_err(("some type error",));
    assert!(err.is_instance_of::<PyTypeError>(py));
    assert_eq!(err.value(py).to_string(), "some type error");
});

pub fn value_bound<'py>(&self, py: Python<'py>) -> &Bound<'py, PyBaseException>

👎Deprecated since 0.23.0: renamed to PyErr::value

Deprecated name for PyErr::value.

pub fn into_value(self, py: Python<'_>) -> Py<PyBaseException>

Consumes self to take ownership of the exception value contained in this error.

pub fn traceback<'py>(&self, py: Python<'py>) -> Option<Bound<'py, PyTraceback>>

Returns the traceback of this exception object.

Examples

use pyo3::{exceptions::PyTypeError, Python};

Python::with_gil(|py| {
    let err = PyTypeError::new_err(("some type error",));
    assert!(err.traceback(py).is_none());
});

pub fn traceback_bound<'py>( &self, py: Python<'py>, ) -> Option<Bound<'py, PyTraceback>>

👎Deprecated since 0.23.0: renamed to PyErr::traceback

Deprecated name for PyErr::traceback.

pub fn occurred(_: Python<'_>) -> bool

Gets whether an error is present in the Python interpreter’s global state.

pub fn take(py: Python<'_>) -> Option<PyErr>

Takes the current error from the Python interpreter’s global state and clears the global state. If no error is set, returns None.

If the error is a PanicException (which would have originated from a panic in a pyo3 callback) then this function will resume the panic.

Use this function when it is not known if an error should be present. If the error is expected to have been set, for example from PyErr::occurred or by an error return value from a C FFI function, use PyErr::fetch.

pub fn fetch(py: Python<'_>) -> PyErr

Equivalent to PyErr::take, but when no error is set:

• Panics in debug mode.
• Returns a SystemError in release mode.

This behavior is consistent with Python’s internal handling of what happens when a C return value indicates an error occurred but the global error state is empty. (A lack of exception should be treated as a bug in the code which returned an error code but did not set an exception.)

Use this function when the error is expected to have been set, for example from PyErr::occurred or by an error return value from a C FFI function.

pub fn new_type<'py>( py: Python<'py>, name: &CStr, doc: Option<&CStr>, base: Option<&Bound<'py, PyType>>, dict: Option<Py<PyAny>>, ) -> Result<Py<PyType>, PyErr>

Creates a new exception type with the given name and docstring.

• base can be an existing exception type to subclass, or a tuple of classes.
• dict specifies an optional dictionary of class variables and methods.
• doc will be the docstring seen by python users.

Errors

This function returns an error if name is not of the form <module>.<ExceptionName>.

pub fn new_type_bound<'py>( py: Python<'py>, name: &str, doc: Option<&str>, base: Option<&Bound<'py, PyType>>, dict: Option<Py<PyAny>>, ) -> Result<Py<PyType>, PyErr>

👎Deprecated since 0.23.0: renamed to PyErr::new_type

Deprecated name for PyErr::new_type.

pub fn display(&self, py: Python<'_>)

Prints a standard traceback to sys.stderr.

pub fn print(&self, py: Python<'_>)

Calls sys.excepthook and then prints a standard traceback to sys.stderr.

pub fn print_and_set_sys_last_vars(&self, py: Python<'_>)

Calls sys.excepthook and then prints a standard traceback to sys.stderr.

Additionally sets sys.last_{type,value,traceback,exc} attributes to this exception.

pub fn matches<'py, T>( &self, py: Python<'py>, exc: T, ) -> Result<bool, <T as IntoPyObject<'py>>::Error>

where T: IntoPyObject<'py>,

Returns true if the current exception matches the exception in exc.

If exc is a class object, this also returns true when self is an instance of a subclass. If exc is a tuple, all exceptions in the tuple (and recursively in subtuples) are searched for a match.

pub fn is_instance(&self, py: Python<'_>, ty: &Bound<'_, PyAny>) -> bool

Returns true if the current exception is instance of T.

pub fn is_instance_bound(&self, py: Python<'_>, ty: &Bound<'_, PyAny>) -> bool

👎Deprecated since 0.23.0: renamed to PyErr::is_instance

Deprecated name for PyErr::is_instance.

pub fn is_instance_of<T>(&self, py: Python<'_>) -> bool

where T: PyTypeInfo,

Returns true if the current exception is instance of T.

pub fn restore(self, py: Python<'_>)

Writes the error back to the Python interpreter’s global state. This is the opposite of PyErr::fetch().

pub fn write_unraisable(self, py: Python<'_>, obj: Option<&Bound<'_, PyAny>>)

Reports the error as unraisable.

This calls sys.unraisablehook() using the current exception and obj argument.

This method is useful to report errors in situations where there is no good mechanism to report back to the Python land. In Python this is used to indicate errors in background threads or destructors which are protected. In Rust code this is commonly useful when you are calling into a Python callback which might fail, but there is no obvious way to handle this error other than logging it.

Calling this method has the benefit that the error goes back into a standardized callback in Python which for instance allows unittests to ensure that no unraisable error actually happend by hooking sys.unraisablehook.

Example:

Python::with_gil(|py| {
    match failing_function() {
        Err(pyerr) => pyerr.write_unraisable(py, None),
        Ok(..) => { /* do something here */ }
    }
    Ok(())
})

pub fn write_unraisable_bound( self, py: Python<'_>, obj: Option<&Bound<'_, PyAny>>, )

👎Deprecated since 0.23.0: renamed to PyErr::write_unraisable

Deprecated name for PyErr::write_unraisable.

pub fn warn<'py>( py: Python<'py>, category: &Bound<'py, PyAny>, message: &CStr, stacklevel: i32, ) -> Result<(), PyErr>

Issues a warning message.

May return an Err(PyErr) if warnings-as-errors is enabled.

Equivalent to warnings.warn() in Python.

The category should be one of the Warning classes available in pyo3::exceptions, or a subclass. The Python object can be retrieved using Python::get_type_bound().

Example:

Python::with_gil(|py| {
    let user_warning = py.get_type::<pyo3::exceptions::PyUserWarning>();
    PyErr::warn(py, &user_warning, c_str!("I am warning you"), 0)?;
    Ok(())
})

pub fn warn_bound<'py>( py: Python<'py>, category: &Bound<'py, PyAny>, message: &str, stacklevel: i32, ) -> Result<(), PyErr>

👎Deprecated since 0.23.0: renamed to PyErr::warn

Deprecated name for PyErr::warn.

pub fn warn_explicit<'py>( py: Python<'py>, category: &Bound<'py, PyAny>, message: &CStr, filename: &CStr, lineno: i32, module: Option<&CStr>, registry: Option<&Bound<'py, PyAny>>, ) -> Result<(), PyErr>

Issues a warning message, with more control over the warning attributes.

May return a PyErr if warnings-as-errors is enabled.

Equivalent to warnings.warn_explicit() in Python.

The category should be one of the Warning classes available in pyo3::exceptions, or a subclass.

pub fn warn_explicit_bound<'py>( py: Python<'py>, category: &Bound<'py, PyAny>, message: &str, filename: &str, lineno: i32, module: Option<&str>, registry: Option<&Bound<'py, PyAny>>, ) -> Result<(), PyErr>

👎Deprecated since 0.23.0: renamed to PyErr::warn

Deprecated name for PyErr::warn_explicit.

pub fn clone_ref(&self, py: Python<'_>) -> PyErr

Clone the PyErr. This requires the GIL, which is why PyErr does not implement Clone.

Examples

use pyo3::{exceptions::PyTypeError, PyErr, Python, prelude::PyAnyMethods};
Python::with_gil(|py| {
    let err: PyErr = PyTypeError::new_err(("some type error",));
    let err_clone = err.clone_ref(py);
    assert!(err.get_type(py).is(&err_clone.get_type(py)));
    assert!(err.value(py).is(err_clone.value(py)));
    match err.traceback(py) {
        None => assert!(err_clone.traceback(py).is_none()),
        Some(tb) => assert!(err_clone.traceback(py).unwrap().is(&tb)),
    }
});

pub fn cause(&self, py: Python<'_>) -> Option<PyErr>

Return the cause (either an exception instance, or None, set by raise ... from ...) associated with the exception, as accessible from Python through __cause__.

pub fn set_cause(&self, py: Python<'_>, cause: Option<PyErr>)

Set the cause associated with the exception, pass None to clear it.

Trait Implementations

impl Debug for PyErr

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Display for PyErr

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Error for PyErr

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn description(&self) -> &str

👎Deprecated since 1.42.0: use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type-based access to context intended for error reports.

impl From<AddrParseError> for PyErr

fn from(err: AddrParseError) -> PyErr

Converts to this type from the input type.

impl<'py, T> From<Bound<'py, T>> for PyErr

where T: ToPyErr,

fn from(err: Bound<'py, T>) -> PyErr

Converts to this type from the input type.

impl From<DecodeUtf16Error> for PyErr

fn from(err: DecodeUtf16Error) -> PyErr

Converts to this type from the input type.

impl From<DowncastError<'_, '_>> for PyErr

Convert DowncastError to Python TypeError.

fn from(err: DowncastError<'_, '_>) -> PyErr

Converts to this type from the input type.

impl From<DowncastIntoError<'_>> for PyErr

Convert DowncastIntoError to Python TypeError.

fn from(err: DowncastIntoError<'_>) -> PyErr

Converts to this type from the input type.

impl From<Error> for PyErr

Create PyErr from io::Error (OSError except if the io::Error is wrapping a Python exception, in this case the exception is returned)

fn from(err: Error) -> PyErr

Converts to this type from the input type.

impl From<FromUtf16Error> for PyErr

fn from(err: FromUtf16Error) -> PyErr

Converts to this type from the input type.

impl From<FromUtf8Error> for PyErr

fn from(err: FromUtf8Error) -> PyErr

Converts to this type from the input type.

impl From<Infallible> for PyErr

fn from(_: Infallible) -> PyErr

Converts to this type from the input type.

impl<W> From<IntoInnerError<W>> for PyErr

fn from(err: IntoInnerError<W>) -> PyErr

Converts to this type from the input type.

impl From<IntoStringError> for PyErr

fn from(err: IntoStringError) -> PyErr

Converts to this type from the input type.

impl From<NulError> for PyErr

fn from(err: NulError) -> PyErr

Converts to this type from the input type.

impl From<ParseBoolError> for PyErr

fn from(err: ParseBoolError) -> PyErr

Converts to this type from the input type.

impl From<ParseFloatError> for PyErr

fn from(err: ParseFloatError) -> PyErr

Converts to this type from the input type.

impl From<ParseIntError> for PyErr

fn from(err: ParseIntError) -> PyErr

Converts to this type from the input type.

impl From<PyBorrowError> for PyErr

fn from(other: PyBorrowError) -> PyErr

Converts to this type from the input type.

impl From<PyBorrowMutError> for PyErr

fn from(other: PyBorrowMutError) -> PyErr

Converts to this type from the input type.

impl From<PyErr> for Error

Convert PyErr to io::Error

fn from(err: PyErr) -> Error

Converts to this type from the input type.

impl From<TryFromIntError> for PyErr

fn from(err: TryFromIntError) -> PyErr

Converts to this type from the input type.

impl From<TryFromSliceError> for PyErr

fn from(err: TryFromSliceError) -> PyErr

Converts to this type from the input type.

impl From<Utf8Error> for PyErr

fn from(err: Utf8Error) -> PyErr

Converts to this type from the input type.

impl IntoPy<Py<PyAny>> for &PyErr

fn into_py(self, py: Python<'_>) -> Py<PyAny>

👎Deprecated since 0.23.0: IntoPy is going to be replaced by IntoPyObject. See the migration guide (https://pyo3.rs/v0.23.0/migration) for more information.

Performs the conversion.

impl IntoPy<Py<PyAny>> for PyErr

fn into_py(self, py: Python<'_>) -> Py<PyAny>

👎Deprecated since 0.23.0: IntoPy is going to be replaced by IntoPyObject. See the migration guide (https://pyo3.rs/v0.23.0/migration) for more information.

Performs the conversion.

impl<'py> IntoPyObject<'py> for &PyErr

type Target = PyBaseException

The Python output type

type Output = Bound<'py, <&PyErr as IntoPyObject<'py>>::Target>

The smart pointer type to use.

type Error = Infallible

The type returned in the event of a conversion error.

fn into_pyobject( self, py: Python<'py>, ) -> Result<<&PyErr as IntoPyObject<'py>>::Output, <&PyErr as IntoPyObject<'py>>::Error>

Performs the conversion.

impl<'py> IntoPyObject<'py> for PyErr

type Target = PyBaseException

The Python output type

type Output = Bound<'py, <PyErr as IntoPyObject<'py>>::Target>

The smart pointer type to use.

type Error = Infallible

The type returned in the event of a conversion error.

fn into_pyobject( self, py: Python<'py>, ) -> Result<<PyErr as IntoPyObject<'py>>::Output, <PyErr as IntoPyObject<'py>>::Error>

Performs the conversion.

impl ToPyObject for PyErr

fn to_object(&self, py: Python<'_>) -> Py<PyAny>

👎Deprecated since 0.23.0: ToPyObject is going to be replaced by IntoPyObject. See the migration guide (https://pyo3.rs/v0.23.0/migration) for more information.

Converts self into a Python object.