first pass at fix

Author: sydney-runkle

python/pydantic_core/core_schema.py

@@ -3964,6 +3964,7 @@ def definition_reference_schema(
     'no_such_attribute',
     'json_invalid',
     'json_type',
+    'cannot_validate_from_json',
     'recursion_loop',
     'missing',
     'frozen_field',

src/errors/types.rs

@@ -167,6 +167,7 @@ error_types! {
         error: {ctx_type: String, ctx_fn: field_from_context},
     },
     JsonType {},
+    CannotValidateFromJson { method_name: {ctx_type: String, ctx_fn: field_from_context} },
     // ---------------------
     // recursion error
     RecursionLoop {},
@@ -477,6 +478,7 @@ impl ErrorType {
             Self::NoSuchAttribute {..} => "Object has no attribute '{attribute}'",
             Self::JsonInvalid {..} => "Invalid JSON: {error}",
             Self::JsonType {..} => "JSON input should be string, bytes or bytearray",
+            Self::CannotValidateFromJson {..} => "Cannot check `{method_name}` when validating from json, use a JsonOrPython validator instead",
             Self::RecursionLoop {..} => "Recursion error - cyclic reference detected",
             Self::Missing {..} => "Field required",
             Self::FrozenField {..} => "Field is frozen",
@@ -626,6 +628,7 @@ impl ErrorType {
         match self {
             Self::NoSuchAttribute { attribute, .. } => render!(tmpl, attribute),
             Self::JsonInvalid { error, .. } => render!(tmpl, error),
+            Self::CannotValidateFromJson { method_name, .. } => render!(tmpl, method_name),
             Self::GetAttributeError { error, .. } => render!(tmpl, error),
             Self::ModelType { class_name, .. } => render!(tmpl, class_name),
             Self::DataclassType { class_name, .. } => render!(tmpl, class_name),

src/validators/is_instance.rs

@@ -1,4 +1,3 @@
-use pyo3::exceptions::PyNotImplementedError;
 use pyo3::intern;
 use pyo3::prelude::*;
 use pyo3::types::{PyDict, PyType};
@@ -56,10 +55,14 @@ impl Validator for IsInstanceValidator {
         _state: &mut ValidationState<'_, 'py>,
     ) -> ValResult<PyObject> {
         let Some(obj) = input.as_python() else {
-            return Err(ValError::InternalErr(PyNotImplementedError::new_err(
-                "Cannot check isinstance when validating from json, \
-                            use a JsonOrPython validator instead.",
-            )));
+            let method_name = "isinstance".to_string();
+            return Err(ValError::new(
+                ErrorType::CannotValidateFromJson {
+                    context: None,
+                    method_name,
+                },
+                input,
+            ));
         };
         match obj.is_instance(self.class.bind(py))? {
             true => Ok(obj.clone().unbind()),

src/validators/is_subclass.rs

@@ -1,4 +1,3 @@
-use pyo3::exceptions::PyNotImplementedError;
 use pyo3::intern;
 use pyo3::prelude::*;
 use pyo3::types::{PyDict, PyType};
@@ -51,10 +50,14 @@ impl Validator for IsSubclassValidator {
         _state: &mut ValidationState<'_, 'py>,
     ) -> ValResult<PyObject> {
         let Some(obj) = input.as_python() else {
-            return Err(ValError::InternalErr(PyNotImplementedError::new_err(
-                "Cannot check issubclass when validating from json, \
-                            use a JsonOrPython validator instead.",
-            )));
+            let method_name = "issubclass".to_string();
+            return Err(ValError::new(
+                ErrorType::CannotValidateFromJson {
+                    context: None,
+                    method_name,
+                },
+                input,
+            ));
         };
         match obj.downcast::<PyType>() {
             Ok(py_type) if py_type.is_subclass(self.class.bind(py))? => Ok(obj.clone().unbind()),