Struct pyo3::exceptions::PyValueError

pub struct PyValueError(_);

Represents Python’s ValueError exception.

Example: Raising ValueError from Rust

This exception can be sent to Python code by converting it into a PyErr, where Python code can then catch it.

use pyo3::prelude::*;
use pyo3::exceptions::PyValueError;

#[pyfunction]
fn always_throws() -> PyResult<()> {
    let message = "I'm ValueError, and I was raised from Rust.";
    Err(PyValueError::new_err(message))
}

Python code:

from my_module import always_throws

try:
   always_throws()
except ValueError as e:
   print(f"Caught an exception: {e}")

Example: Catching ValueError in Rust

use pyo3::prelude::*;
use pyo3::exceptions::PyValueError;

Python::with_gil(|py| {
    let result: PyResult<()> = py.run("raise ValueError", None, None);

    let error_type = match result {
        Ok(_) => "Not an error",
        Err(error) if error.is_instance_of::<PyValueError>(py) => "ValueError",
        Err(_) => "Some other error",
    };

    assert_eq!(error_type, "ValueError");
});

Implementations

impl PyValueError

pub fn new_err<A>(args: A) -> PyErrwhere A: PyErrArguments + Send + Sync + 'static,

Creates a new PyErr of this type.

Methods from Deref<Target = PyAny>

pub fn is<T: AsPyPointer>(&self, other: &T) -> bool

Returns whether self and other point to the same object. To compare the equality of two objects (the == operator), use eq.

This is equivalent to the Python expression self is other.

pub fn hasattr<N>(&self, attr_name: N) -> PyResult<bool>where N: IntoPy<Py<PyString>>,

Determines whether this object has the given attribute.

This is equivalent to the Python expression hasattr(self, attr_name).

To avoid repeated temporary allocations of Python strings, the intern! macro can be used to intern attr_name.

Example: intern!ing the attribute name

#[pyfunction]
fn has_version(sys: &PyModule) -> PyResult<bool> {
    sys.hasattr(intern!(sys.py(), "version"))
}

pub fn getattr<N>(&self, attr_name: N) -> PyResult<&PyAny>where N: IntoPy<Py<PyString>>,

Retrieves an attribute value.

This is equivalent to the Python expression self.attr_name.

To avoid repeated temporary allocations of Python strings, the intern! macro can be used to intern attr_name.

Example: intern!ing the attribute name

#[pyfunction]
fn version(sys: &PyModule) -> PyResult<&PyAny> {
    sys.getattr(intern!(sys.py(), "version"))
}

pub fn setattr<N, V>(&self, attr_name: N, value: V) -> PyResult<()>where N: IntoPy<Py<PyString>>, V: ToPyObject,

Sets an attribute value.

This is equivalent to the Python expression self.attr_name = value.

To avoid repeated temporary allocations of Python strings, the intern! macro can be used to intern name.

Example: intern!ing the attribute name

#[pyfunction]
fn set_answer(ob: &PyAny) -> PyResult<()> {
    ob.setattr(intern!(ob.py(), "answer"), 42)
}

pub fn delattr<N>(&self, attr_name: N) -> PyResult<()>where N: IntoPy<Py<PyString>>,

Deletes an attribute.

This is equivalent to the Python statement del self.attr_name.

To avoid repeated temporary allocations of Python strings, the intern! macro can be used to intern attr_name.

pub fn compare<O>(&self, other: O) -> PyResult<Ordering>where O: ToPyObject,

Returns an Ordering between self and other.

This is equivalent to the following Python code:

if self == other:
    return Equal
elif a < b:
    return Less
elif a > b:
    return Greater
else:
    raise TypeError("PyAny::compare(): All comparisons returned false")

Examples

use pyo3::prelude::*;
use pyo3::types::PyFloat;
use std::cmp::Ordering;

Python::with_gil(|py| -> PyResult<()> {
    let a = PyFloat::new(py, 0_f64);
    let b = PyFloat::new(py, 42_f64);
    assert_eq!(a.compare(b)?, Ordering::Less);
    Ok(())
})?;

It will return PyErr for values that cannot be compared:

use pyo3::prelude::*;
use pyo3::types::{PyFloat, PyString};

Python::with_gil(|py| -> PyResult<()> {
    let a = PyFloat::new(py, 0_f64);
    let b = PyString::new(py, "zero");
    assert!(a.compare(b).is_err());
    Ok(())
})?;

pub fn rich_compare<O>( &self, other: O, compare_op: CompareOp ) -> PyResult<&PyAny>where O: ToPyObject,

Tests whether two Python objects obey a given CompareOp.

lt, le, eq, ne, gt and ge are the specialized versions of this function.

Depending on the value of compare_op, this is equivalent to one of the following Python expressions:

compare_op	Python expression
CompareOp::Eq	self == other
CompareOp::Ne	self != other
CompareOp::Lt	self < other
CompareOp::Le	self <= other
CompareOp::Gt	self > other
CompareOp::Ge	self >= other

Examples

use pyo3::class::basic::CompareOp;
use pyo3::prelude::*;
use pyo3::types::PyInt;

Python::with_gil(|py| -> PyResult<()> {
    let a: &PyInt = 0_u8.into_py(py).into_ref(py).downcast()?;
    let b: &PyInt = 42_u8.into_py(py).into_ref(py).downcast()?;
    assert!(a.rich_compare(b, CompareOp::Le)?.is_true()?);
    Ok(())
})?;

pub fn lt<O>(&self, other: O) -> PyResult<bool>where O: ToPyObject,

Tests whether this object is less than another.

This is equivalent to the Python expression self < other.

pub fn le<O>(&self, other: O) -> PyResult<bool>where O: ToPyObject,

Tests whether this object is less than or equal to another.

This is equivalent to the Python expression self <= other.

pub fn eq<O>(&self, other: O) -> PyResult<bool>where O: ToPyObject,

Tests whether this object is equal to another.

This is equivalent to the Python expression self == other.

pub fn ne<O>(&self, other: O) -> PyResult<bool>where O: ToPyObject,

Tests whether this object is not equal to another.

This is equivalent to the Python expression self != other.

pub fn gt<O>(&self, other: O) -> PyResult<bool>where O: ToPyObject,

Tests whether this object is greater than another.

This is equivalent to the Python expression self > other.

pub fn ge<O>(&self, other: O) -> PyResult<bool>where O: ToPyObject,

Tests whether this object is greater than or equal to another.

This is equivalent to the Python expression self >= other.

pub fn is_callable(&self) -> bool

Determines whether this object appears callable.

This is equivalent to Python’s callable() function.

Examples

use pyo3::prelude::*;

Python::with_gil(|py| -> PyResult<()> {
    let builtins = PyModule::import(py, "builtins")?;
    let print = builtins.getattr("print")?;
    assert!(print.is_callable());
    Ok(())
})?;

This is equivalent to the Python statement assert callable(print).

Note that unless an API needs to distinguish between callable and non-callable objects, there is no point in checking for callability. Instead, it is better to just do the call and handle potential exceptions.

pub fn call( &self, args: impl IntoPy<Py<PyTuple>>, kwargs: Option<&PyDict> ) -> PyResult<&PyAny>

Calls the object.

This is equivalent to the Python expression self(*args, **kwargs).

Examples

use pyo3::prelude::*;
use pyo3::types::PyDict;

const CODE: &str = r#"
def function(*args, **kwargs):
    assert args == ("hello",)
    assert kwargs == {"cruel": "world"}
    return "called with args and kwargs"
"#;

Python::with_gil(|py| {
    let module = PyModule::from_code(py, CODE, "", "")?;
    let fun = module.getattr("function")?;
    let args = ("hello",);
    let kwargs = PyDict::new(py);
    kwargs.set_item("cruel", "world")?;
    let result = fun.call(args, Some(kwargs))?;
    assert_eq!(result.extract::<&str>()?, "called with args and kwargs");
    Ok(())
})

pub fn call0(&self) -> PyResult<&PyAny>

Calls the object without arguments.

This is equivalent to the Python expression self().

Examples

use pyo3::prelude::*;

Python::with_gil(|py| -> PyResult<()> {
    let module = PyModule::import(py, "builtins")?;
    let help = module.getattr("help")?;
    help.call0()?;
    Ok(())
})?;

This is equivalent to the Python expression help().

pub fn call1(&self, args: impl IntoPy<Py<PyTuple>>) -> PyResult<&PyAny>

Calls the object with only positional arguments.

This is equivalent to the Python expression self(*args).

Examples

use pyo3::prelude::*;

const CODE: &str = r#"
def function(*args, **kwargs):
    assert args == ("hello",)
    assert kwargs == {}
    return "called with args"
"#;

Python::with_gil(|py| {
    let module = PyModule::from_code(py, CODE, "", "")?;
    let fun = module.getattr("function")?;
    let args = ("hello",);
    let result = fun.call1(args)?;
    assert_eq!(result.extract::<&str>()?, "called with args");
    Ok(())
})

pub fn call_method<N, A>( &self, name: N, args: A, kwargs: Option<&PyDict> ) -> PyResult<&PyAny>where N: IntoPy<Py<PyString>>, A: IntoPy<Py<PyTuple>>,

Calls a method on the object.

This is equivalent to the Python expression self.name(*args, **kwargs).

To avoid repeated temporary allocations of Python strings, the intern! macro can be used to intern name.

Examples

use pyo3::prelude::*;
use pyo3::types::PyDict;

const CODE: &str = r#"
class A:
    def method(self, *args, **kwargs):
        assert args == ("hello",)
        assert kwargs == {"cruel": "world"}
        return "called with args and kwargs"
a = A()
"#;

Python::with_gil(|py| {
    let module = PyModule::from_code(py, CODE, "", "")?;
    let instance = module.getattr("a")?;
    let args = ("hello",);
    let kwargs = PyDict::new(py);
    kwargs.set_item("cruel", "world")?;
    let result = instance.call_method("method", args, Some(kwargs))?;
    assert_eq!(result.extract::<&str>()?, "called with args and kwargs");
    Ok(())
})

pub fn call_method0<N>(&self, name: N) -> PyResult<&PyAny>where N: IntoPy<Py<PyString>>,

Calls a method on the object without arguments.

This is equivalent to the Python expression self.name().

To avoid repeated temporary allocations of Python strings, the intern! macro can be used to intern name.

Examples

use pyo3::prelude::*;

const CODE: &str = r#"
class A:
    def method(self, *args, **kwargs):
        assert args == ()
        assert kwargs == {}
        return "called with no arguments"
a = A()
"#;

Python::with_gil(|py| {
    let module = PyModule::from_code(py, CODE, "", "")?;
    let instance = module.getattr("a")?;
    let result = instance.call_method0("method")?;
    assert_eq!(result.extract::<&str>()?, "called with no arguments");
    Ok(())
})

pub fn call_method1<N, A>(&self, name: N, args: A) -> PyResult<&PyAny>where N: IntoPy<Py<PyString>>, A: IntoPy<Py<PyTuple>>,

Calls a method on the object with only positional arguments.

This is equivalent to the Python expression self.name(*args).

To avoid repeated temporary allocations of Python strings, the intern! macro can be used to intern name.

Examples

use pyo3::prelude::*;

const CODE: &str = r#"
class A:
    def method(self, *args, **kwargs):
        assert args == ("hello",)
        assert kwargs == {}
        return "called with args"
a = A()
"#;

Python::with_gil(|py| {
    let module = PyModule::from_code(py, CODE, "", "")?;
    let instance = module.getattr("a")?;
    let args = ("hello",);
    let result = instance.call_method1("method", args)?;
    assert_eq!(result.extract::<&str>()?, "called with args");
    Ok(())
})

pub fn is_true(&self) -> PyResult<bool>

Returns whether the object is considered to be true.

This is equivalent to the Python expression bool(self).

pub fn is_none(&self) -> bool

Returns whether the object is considered to be None.

This is equivalent to the Python expression self is None.

pub fn is_ellipsis(&self) -> bool

Returns whether the object is Ellipsis, e.g. ....

This is equivalent to the Python expression self is ....

pub fn is_empty(&self) -> PyResult<bool>

Returns true if the sequence or mapping has a length of 0.

This is equivalent to the Python expression len(self) == 0.

pub fn get_item<K>(&self, key: K) -> PyResult<&PyAny>where K: ToPyObject,

Gets an item from the collection.

This is equivalent to the Python expression self[key].

pub fn set_item<K, V>(&self, key: K, value: V) -> PyResult<()>where K: ToPyObject, V: ToPyObject,

Sets a collection item value.

This is equivalent to the Python expression self[key] = value.

pub fn del_item<K>(&self, key: K) -> PyResult<()>where K: ToPyObject,

Deletes an item from the collection.

This is equivalent to the Python expression del self[key].

pub fn iter(&self) -> PyResult<&PyIterator>

Takes an object and returns an iterator for it.

This is typically a new iterator but if the argument is an iterator, this returns itself.

pub fn get_type(&self) -> &PyType

Returns the Python type object for this object’s type.

pub fn get_type_ptr(&self) -> *mut PyTypeObject

Returns the Python type pointer for this object.

pub fn cast_as<'a, D>(&'a self) -> Result<&'a D, PyDowncastError<'_>>where D: PyTryFrom<'a>,

👎Deprecated since 0.18.0: use the equivalent .downcast()

Converts this PyAny to a concrete Python type.

pub fn downcast<'p, T>(&'p self) -> Result<&'p T, PyDowncastError<'_>>where T: PyTryFrom<'p>,

Downcast this PyAny to a concrete Python type or pyclass.

Note that you can often avoid downcasting yourself by just specifying the desired type in function or method signatures. However, manual downcasting is sometimes necessary.

For extracting a Rust-only type, see PyAny::extract.

Example: Downcasting to a specific Python object

use pyo3::prelude::*;
use pyo3::types::{PyDict, PyList};

Python::with_gil(|py| {
    let dict = PyDict::new(py);
    assert!(dict.is_instance_of::<PyAny>());
    let any: &PyAny = dict.as_ref();

    assert!(any.downcast::<PyDict>().is_ok());
    assert!(any.downcast::<PyList>().is_err());
});

Example: Getting a reference to a pyclass

This is useful if you want to mutate a PyObject that might actually be a pyclass.

use pyo3::prelude::*;

#[pyclass]
struct Class {
    i: i32,
}

Python::with_gil(|py| {
    let class: &PyAny = Py::new(py, Class { i: 0 }).unwrap().into_ref(py);

    let class_cell: &PyCell<Class> = class.downcast()?;

    class_cell.borrow_mut().i += 1;

    // Alternatively you can get a `PyRefMut` directly
    let class_ref: PyRefMut<'_, Class> = class.extract()?;
    assert_eq!(class_ref.i, 1);
    Ok(())
})

pub fn downcast_exact<'p, T>(&'p self) -> Result<&'p T, PyDowncastError<'_>>where T: PyTryFrom<'p>,

Downcast this PyAny to a concrete Python type or pyclass (but not a subclass of it).

It is almost always better to use PyAny::downcast because it accounts for Python subtyping. Use this method only when you do not want to allow subtypes.

The advantage of this method over PyAny::downcast is that it is faster. The implementation of downcast_exact uses the equivalent of the Python expression type(self) is T, whereas downcast uses isinstance(self, T).

For extracting a Rust-only type, see PyAny::extract.

Example: Downcasting to a specific Python object but not a subtype

use pyo3::prelude::*;
use pyo3::types::{PyBool, PyLong};

Python::with_gil(|py| {
    let b = PyBool::new(py, true);
    assert!(b.is_instance_of::<PyBool>());
    let any: &PyAny = b.as_ref();

    // `bool` is a subtype of `int`, so `downcast` will accept a `bool` as an `int`
    // but `downcast_exact` will not.
    assert!(any.downcast::<PyLong>().is_ok());
    assert!(any.downcast_exact::<PyLong>().is_err());

    assert!(any.downcast_exact::<PyBool>().is_ok());
});

pub unsafe fn downcast_unchecked<'p, T>(&'p self) -> &'p Twhere T: PyTryFrom<'p>,

Converts this PyAny to a concrete Python type without checking validity.

Safety

Callers must ensure that the type is valid or risk type confusion.

pub fn extract<'a, D>(&'a self) -> PyResult<D>where D: FromPyObject<'a>,

Extracts some type from the Python object.

This is a wrapper function around FromPyObject::extract().

pub fn get_refcnt(&self) -> isize

Returns the reference count for the Python object.

pub fn repr(&self) -> PyResult<&PyString>

Computes the “repr” representation of self.

This is equivalent to the Python expression repr(self).

pub fn str(&self) -> PyResult<&PyString>

Computes the “str” representation of self.

This is equivalent to the Python expression str(self).

pub fn hash(&self) -> PyResult<isize>

Retrieves the hash code of self.

This is equivalent to the Python expression hash(self).

pub fn len(&self) -> PyResult<usize>

Returns the length of the sequence or mapping.

This is equivalent to the Python expression len(self).

pub fn dir(&self) -> &PyList

Returns the list of attributes of this object.

This is equivalent to the Python expression dir(self).

pub fn is_instance(&self, ty: &PyAny) -> PyResult<bool>

Checks whether this object is an instance of type ty.

This is equivalent to the Python expression isinstance(self, ty).

pub fn is_exact_instance(&self, ty: &PyAny) -> bool

Checks whether this object is an instance of exactly type ty (not a subclass).

This is equivalent to the Python expression type(self) is ty.

pub fn is_instance_of<T: PyTypeInfo>(&self) -> bool

Checks whether this object is an instance of type T.

This is equivalent to the Python expression isinstance(self, T), if the type T is known at compile time.

pub fn is_exact_instance_of<T: PyTypeInfo>(&self) -> bool

Checks whether this object is an instance of exactly type T.

This is equivalent to the Python expression type(self) is T, if the type T is known at compile time.

pub fn contains<V>(&self, value: V) -> PyResult<bool>where V: ToPyObject,

Determines if self contains value.

This is equivalent to the Python expression value in self.

pub fn py(&self) -> Python<'_>

Returns a GIL marker constrained to the lifetime of this type.

pub fn py_super(&self) -> PyResult<&PySuper>

Available on non-PyPy only.

Return a proxy object that delegates method calls to a parent or sibling class of type.

This is equivalent to the Python expression super()

Trait Implementations

impl AsPyPointer for PyValueError

fn as_ptr(&self) -> *mut PyObject

Gets the underlying FFI pointer, returns a borrowed pointer.

impl AsRef<PyAny> for PyValueError

fn as_ref(&self) -> &PyAny

Converts this type into a shared reference of the (usually inferred) input type.

impl Debug for PyValueError

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

Formats the value using the given formatter.

impl Deref for PyValueError

type Target = PyAny

The resulting type after dereferencing.

fn deref(&self) -> &PyAny

Dereferences the value.

impl Display for PyValueError

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

Formats the value using the given formatter.

impl Error for PyValueError

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

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, demand: &mut Demand<'a>)

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

Provides type based access to context intended for error reports.

impl<'a> From<&'a PyValueError> for &'a PyAny

fn from(ob: &'a PyValueError) -> Self

Converts to this type from the input type.

impl From<&PyValueError> for Py<PyValueError>

fn from(other: &PyValueError) -> Self

Converts to this type from the input type.

impl From<&PyValueError> for PyErr

fn from(err: &PyValueError) -> PyErr

Converts to this type from the input type.

impl<'py> FromPyObject<'py> for &'py PyValueError

fn extract(obj: &'py PyAny) -> PyResult<Self>

Extracts Self from the source PyObject.

impl IntoPy<Py<PyValueError>> for &PyValueError

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

Performs the conversion.

impl PyNativeType for PyValueError

fn py(&self) -> Python<'_>

Returns a GIL marker constrained to the lifetime of this type.

unsafe fn unchecked_downcast(obj: &PyAny) -> &Self

Cast &PyAny to &Self without no type checking.

impl PyTypeInfo for PyValueError

type AsRefTarget = PyValueError

Utility type to make Py::as_ref work.

const NAME: &'static str = _

Class name.

const MODULE: Option<&'static str> = _

Module name, if any.

fn type_object_raw(_py: Python<'_>) -> *mut PyTypeObject

Returns the PyTypeObject instance for this type.

fn type_object(py: Python<'_>) -> &PyType

Returns the safe abstraction over the type object.

fn is_type_of(object: &PyAny) -> bool

Checks if object is an instance of this type or a subclass of this type.

fn is_exact_type_of(object: &PyAny) -> bool

Checks if object is an instance of this type.

impl ToPyObject for PyValueError

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

Converts self into a Python object.

impl PyLayout<PyValueError> for PyBaseExceptionObject

impl PySizedLayout<PyValueError> for PyBaseExceptionObject