fix panic in validate_assignment when field has gone missing (pydantic/pydantic-core#1532)

Original-commit-link: pydantic/pydantic-core@4cb82bf

Author: davidhewitt

src/validators/model_fields.rs

@@ -421,11 +421,16 @@ impl Validator for ModelFieldsValidator {
         let new_extra = match &self.extra_behavior {
             ExtraBehavior::Allow => {
                 let non_extra_data = PyDict::new_bound(py);
-                self.fields.iter().for_each(|f| {
-                    let popped_value = PyAnyMethods::get_item(&**new_data, &f.name).unwrap();
-                    new_data.del_item(&f.name).unwrap();
-                    non_extra_data.set_item(&f.name, popped_value).unwrap();
-                });
+                self.fields.iter().try_for_each(|f| -> PyResult<()> {
+                    let Some(popped_value) = new_data.get_item(&f.name)? else {
+                        // field not present in __dict__ for some reason; let the rest of the
+                        // validation pipeline handle it later
+                        return Ok(());
+                    };
+                    new_data.del_item(&f.name)?;
+                    non_extra_data.set_item(&f.name, popped_value)?;
+                    Ok(())
+                })?;
                 let new_extra = new_data.copy()?;
                 new_data.clear();
                 new_data.update(non_extra_data.as_mapping())?;

tests/validators/test_model.py

@@ -1036,17 +1036,17 @@ def __init__(self):
             self.__pydantic_extra__ = None
 
     v = SchemaValidator(
-        {
-            'type': 'model',
-            'cls': MyModel,
-            'schema': {
-                'type': 'model-fields',
-                'fields': {
-                    'field_a': {'type': 'model-field', 'schema': {'type': 'str'}},
-                    'field_b': {'type': 'model-field', 'schema': {'type': 'int'}},
+        core_schema.model_schema(
+            MyModel,
+            core_schema.model_fields_schema(
+                {
+                    'field_a': core_schema.model_field(core_schema.str_schema()),
+                    'field_b': core_schema.model_field(core_schema.int_schema()),
                 },
-            },
-        }
+                extra_behavior='allow',
+            ),
+            extra_behavior='allow',
+        )
     )
 
     m = MyModel()
@@ -1063,6 +1063,12 @@ def __init__(self):
     v.validate_assignment(m, 'field_b', '322', from_attributes=True)
     assert m.field_b == 322
 
+    # try deleting a field
+    del m.field_b
+    # assignment to `field_a` should not care about `field_b` missing
+    v.validate_assignment(m, 'field_a', 'hello world', from_attributes=True)
+    assert m.field_a == 'hello world'
+
 
 def test_validate_assignment_function():
     class MyModel: