fix: set right default value for required (optional) fields (#2143)

closes #2142

Author: PrettyWood

changes/2142-PrettyWood.md

@@ -0,0 +1 @@
+fix: set right default value for required (optional) fields

pydantic/fields.py

@@ -307,7 +307,7 @@ def infer(
         required: 'BoolUndefined' = Undefined
         if value is Required:
             required = True
-            value = None
+            value = Ellipsis
         elif value is not Undefined:
             required = False
         field_info.alias = field_info.alias or field_info_from_config.get('alias')

tests/test_dataclasses.py

@@ -406,7 +406,7 @@ class User:
     fields = user.__pydantic_model__.__fields__
 
     assert fields['id'].required is True
-    assert fields['id'].default is None
+    assert fields['id'].default is Ellipsis
 
     assert fields['name'].required is False
     assert fields['name'].default == 'John Doe'
@@ -425,7 +425,7 @@ class User:
     fields = user.__pydantic_model__.__fields__
 
     assert fields['id'].required is True
-    assert fields['id'].default is None
+    assert fields['id'].default is Ellipsis
 
     assert fields['aliases'].required is False
     assert fields['aliases'].default == {'John': 'Joey'}

tests/test_main.py

@@ -980,6 +980,35 @@ class Config:
     assert m.dict(exclude_unset=True, by_alias=True) == {'alias_a': 'a', 'c': 'c'}
 
 
+def test_exclude_defaults():
+    class Model(BaseModel):
+        mandatory: str
+        nullable_mandatory: Optional[str] = ...
+        facultative: str = 'x'
+        nullable_facultative: Optional[str] = None
+
+    m = Model(mandatory='a', nullable_mandatory=None)
+    assert m.dict(exclude_defaults=True) == {
+        'mandatory': 'a',
+        'nullable_mandatory': None,
+    }
+
+    m = Model(mandatory='a', nullable_mandatory=None, facultative='y', nullable_facultative=None)
+    assert m.dict(exclude_defaults=True) == {
+        'mandatory': 'a',
+        'nullable_mandatory': None,
+        'facultative': 'y',
+    }
+
+    m = Model(mandatory='a', nullable_mandatory=None, facultative='y', nullable_facultative='z')
+    assert m.dict(exclude_defaults=True) == {
+        'mandatory': 'a',
+        'nullable_mandatory': None,
+        'facultative': 'y',
+        'nullable_facultative': 'z',
+    }
+
+
 def test_dir_fields():
     class MyModel(BaseModel):
         attribute_a: int