feat: raise KeyError when yaml_config_section is missing in YAML file

Author: Seunghan-Jung

pydantic_settings/sources/providers/yaml.py

@@ -55,7 +55,12 @@ def __init__(
         self.yaml_data = self._read_files(self.yaml_file_path)
 
         if self.yaml_config_section:
-            self.yaml_data = self.yaml_data[self.yaml_config_section]
+            try:
+                self.yaml_data = self.yaml_data[self.yaml_config_section]
+            except KeyError:
+                raise KeyError(
+                    f'yaml_config_section key "{self.yaml_config_section}" not found in {self.yaml_file_path}'
+                )
         super().__init__(settings_cls, self.yaml_data)
 
     def _read_file(self, file_path: Path) -> dict[str, Any]:

tests/test_source_yaml.py

@@ -197,3 +197,34 @@ def settings_customise_sources(
 
     s = Settings()
     assert s.nested_field == 'world!'
+
+
+@pytest.mark.skipif(yaml is None, reason='pyYAML is not installed')
+def test_invalid_yaml_config_section(tmp_path):
+    p = tmp_path / '.env'
+    p.write_text(
+        """
+    foobar: "Hello"
+    nested:
+        nested_field: "world!"
+    """
+    )
+
+    class Settings(BaseSettings):
+        nested_field: str
+
+        model_config = SettingsConfigDict(yaml_file=p, yaml_config_section='invalid_key')
+
+        @classmethod
+        def settings_customise_sources(
+            cls,
+            settings_cls: type[BaseSettings],
+            init_settings: PydanticBaseSettingsSource,
+            env_settings: PydanticBaseSettingsSource,
+            dotenv_settings: PydanticBaseSettingsSource,
+            file_secret_settings: PydanticBaseSettingsSource,
+        ) -> tuple[PydanticBaseSettingsSource, ...]:
+            return (YamlConfigSettingsSource(settings_cls),)
+
+    with pytest.raises(KeyError):
+        Settings()