Support for multiple inheritance in create_exception #4979

Activity

1. kylebarron

   added

   enhancement

   on Mar 14, 2025
2. lukasbindreiter commented on Jun 24, 2025

   

   lukasbindreiter

   on Jun 24, 2025

   More actions

   create_exception eventually ends up here:

   pyo3/src/err/mod.rs

   Lines 388 to 400 in e486930

   	/// This function returns an error if `name` is not of the form `<module>.<ExceptionName>`.
   	pub fn new_type<'py>(
   	py: Python<'py>,
   	name: &CStr,
   	doc: Option<&CStr>,
   	base: Option<&Bound<'py, PyType>>,
   	dict: Option<PyObject>,
   	) -> PyResult<Py<PyType>> {
   	let base: *mut ffi::PyObject = match base {
   	None => std::ptr::null_mut(),
   	Some(obj) => obj.as_ptr(),
   	};

   which then in turn calls this C function:

   pyo3/pyo3-ffi/src/pyerrors.rs

   Lines 311 to 316 in e486930

   	pub fn PyErr_NewExceptionWithDoc(
   	name: *const c_char,
   	doc: *const c_char,
   	base: *mut PyObject,
   	dict: *mut PyObject,
   	) -> *mut PyObject;

   The python docs for this function mentions that:

   The base argument can be used to specify alternate base classes; it can either be only one class or a tuple of classes

   So I think multiple base classes for exceptions should in theory be possible.
3. kylebarron commented on Jun 24, 2025

   

   kylebarron

   on Jun 24, 2025

   ContributorAuthor

   More actions

   Yes it should be possible if you using the Python C FFI bindings, but that's too easy to misuse if you don't know Python's C API well, so I'd prefer waiting for a safe wrapper to exist.

   👍React with 👍1Reacted by Lukas Bindreiter
4. lukasbindreiter commented on Jun 25, 2025

   

   lukasbindreiter

   on Jun 25, 2025

   More actions

   Yeah, I was just checking out of curiosity how hard it would be to add support for them in PyO3 (by adapting create_exception or offering a separate function for it) - didn't mean for users of PyO3 to bypass this and go directly to the C API in unsafe rust.

   👍React with 👍1Reacted by Kyle Barron
5. davidhewitt

   added the

   Feature

   issue type on Nov 5, 2025
6. davidhewitt

   removed

   enhancement

   on Nov 5, 2025