Allow nested env var source to override nested init source.

pydantic_settings/sources.py

@@ -7,10 +7,10 @@
 from collections import deque
 from dataclasses import is_dataclass
 from pathlib import Path
-from typing import TYPE_CHECKING, Any, List, Mapping, Sequence, Tuple, Union, cast
+from typing import TYPE_CHECKING, Any, Dict, List, Mapping, Sequence, Tuple, Union, cast
 
 from dotenv import dotenv_values
-from pydantic import AliasChoices, AliasPath, BaseModel, Json
+from pydantic import AliasChoices, AliasPath, BaseModel, Json, TypeAdapter
 from pydantic._internal._typing_extra import origin_is_union
 from pydantic._internal._utils import deep_update, lenient_issubclass
 from pydantic.fields import FieldInfo
@@ -121,7 +121,7 @@ def get_field_value(self, field: FieldInfo, field_name: str) -> tuple[Any, str,
         return None, '', False
 
     def __call__(self) -> dict[str, Any]:
-        return self.init_kwargs
+        return TypeAdapter(Dict[str, Any]).dump_python(self.init_kwargs)
 
     def __repr__(self) -> str:
         return f'InitSettingsSource(init_kwargs={self.init_kwargs!r})'

tests/test_settings.py

@@ -619,6 +619,43 @@ def settings_customise_sources(
     assert s.bar == 'env setting'
 
 
+def test_env_deep_override(env):
+    class DeepSubModel(BaseModel):
+        v4: str
+
+    class SubModel(BaseModel):
+        v1: str
+        v2: bytes
+        v3: int
+        deep: DeepSubModel
+
+    class Settings(BaseSettings, env_nested_delimiter='__'):
+        v0: str
+        sub_model: SubModel
+
+        @classmethod
+        def settings_customise_sources(
+            cls, settings_cls, init_settings, env_settings, dotenv_settings, file_secret_settings
+        ):
+            return env_settings, dotenv_settings, init_settings, file_secret_settings
+
+    env.set('SUB_MODEL__DEEP__V4', 'override-v4')
+
+    s_final = {'v0': '0', 'sub_model': {'v1': 'init-v1', 'v2': b'init-v2', 'v3': 3, 'deep': {'v4': 'override-v4'}}}
+
+    s = Settings(v0='0', sub_model={'v1': 'init-v1', 'v2': b'init-v2', 'v3': 3, 'deep': {'v4': 'init-v4'}})
+    assert s.model_dump() == s_final
+
+    s = Settings(v0='0', sub_model=SubModel(v1='init-v1', v2=b'init-v2', v3=3, deep=DeepSubModel(v4='init-v4')))
+    assert s.model_dump() == s_final
+
+    s = Settings(v0='0', sub_model=SubModel(v1='init-v1', v2=b'init-v2', v3=3, deep={'v4': 'init-v4'}))
+    assert s.model_dump() == s_final
+
+    s = Settings(v0='0', sub_model={'v1': 'init-v1', 'v2': b'init-v2', 'v3': 3, 'deep': DeepSubModel(v4='init-v4')})
+    assert s.model_dump() == s_final
+
+
 def test_config_file_settings_nornir(env):
     """
     See https://github.com/pydantic/pydantic/pull/341#issuecomment-450378771