Strip non-explicit default values. (#692)

Author: kschwab

pydantic_settings/main.py

@@ -426,6 +426,7 @@ def _settings_build_values(
 
         if sources:
             state: dict[str, Any] = {}
+            defaults: dict[str, Any] = {}
             states: dict[str, dict[str, Any]] = {}
             for source in sources:
                 if isinstance(source, PydanticBaseSettingsSource):
@@ -435,8 +436,15 @@ def _settings_build_values(
                 source_name = source.__name__ if hasattr(source, '__name__') else type(source).__name__
                 source_state = source()
 
+                if isinstance(source, DefaultSettingsSource):
+                    defaults = source_state
+
                 states[source_name] = source_state
                 state = deep_update(source_state, state)
+
+            # Strip any default values not explicity set before returning final state
+            state = {key: val for key, val in state.items() if key not in defaults or defaults[key] != val}
+
             return state
         else:
             # no one should mean to do this, but I think returning an empty dict is marginally preferable

tests/test_settings.py

@@ -639,8 +639,27 @@ class SettingsDefaultsA(BaseSettings, env_nested_delimiter='__', nested_model_de
         nested_d: NestedC = NestedC(v0=False, v1=True)
         nested_c: NestedD = NestedD()
 
+    assert SettingsDefaultsA().model_dump() == {
+        'nested_a': {'v0': False, 'v1': True},
+        'nested_b': {'v0': False, 'v1': True},
+        'nested_c': {'v0': False, 'v1': True},
+        'nested_d': {'v0': False, 'v1': True},
+    }
+    assert SettingsDefaultsA().model_dump(exclude_unset=True) == {}
+
     env.set('NESTED_A__V0', 'True')
     env.set('NESTED_B__V0', 'True')
+    assert SettingsDefaultsA().model_dump() == {
+        'nested_a': {'v0': True, 'v1': True},
+        'nested_b': {'v0': True, 'v1': True},
+        'nested_c': {'v0': False, 'v1': True},
+        'nested_d': {'v0': False, 'v1': True},
+    }
+    assert SettingsDefaultsA().model_dump(exclude_unset=True) == {
+        'nested_a': {'v0': True, 'v1': True},
+        'nested_b': {'v0': True, 'v1': True},
+    }
+
     env.set('NESTED_C__V0', 'True')
     env.set('NESTED_D__V0', 'True')
     assert SettingsDefaultsA().model_dump() == {
@@ -649,6 +668,12 @@ class SettingsDefaultsA(BaseSettings, env_nested_delimiter='__', nested_model_de
         'nested_c': {'v0': True, 'v1': True},
         'nested_d': {'v0': True, 'v1': True},
     }
+    assert SettingsDefaultsA().model_dump(exclude_unset=True) == {
+        'nested_a': {'v0': True, 'v1': True},
+        'nested_b': {'v0': True, 'v1': True},
+        'nested_c': {'v0': True, 'v1': True},
+        'nested_d': {'v0': True, 'v1': True},
+    }
 
 
 def test_init_kwargs_nested_model_default_partial_update(env):