simplify Union field choice

pydantic/exceptions.py

@@ -11,7 +11,7 @@ def type_json(type_: type):
             return str(type_)
 
 
-Error = namedtuple('Error', ['exc', 'track_type', 'index'])
+Error = namedtuple('Error', ['exc', 'track', 'index'])
 
 
 def jsonify_errors(e):
@@ -20,7 +20,7 @@ def jsonify_errors(e):
     elif isinstance(e, Error):
         d = {
             'error_type': e.exc.__class__.__name__,
-            'track': type_json(e.track_type),
+            'track': type_json(e.track),
             'index': e.index,
         }
         if isinstance(e.exc, ValidationError):

pydantic/fields.py

@@ -175,20 +175,14 @@ class Field:
             return result, None
 
     def _validate_singleton(self, tracks, v, model, index=None):
-        result, errors = ..., []
+        errors = []
         for track in tracks:
             value, exc = track.validate(v, model, self)
             if exc:
                 errors.append(Error(exc, track.type_, index))
-            elif isinstance(v, track.type_):
-                # exact match: return immediately
-                return value, None
             else:
-                result = value
-        if result is not ...:
-            return result, None
-        else:
-            return v, errors[0] if len(tracks) == 1 else errors
+                return value, None
+        return v, errors[0] if len(tracks) == 1 else errors
 
     def __repr__(self):
         return f'<Field {self}>'
@@ -233,7 +227,7 @@ class ValidatorRoute:
                     v = validator(v, model=model, field=field)
                 else:
                     v = validator(model, v)
-            except (ValueError, TypeError, ImportError) as e:
+            except (ValueError, TypeError) as e:
                 return v, e
         return v, None
 

pydantic/types.py

@@ -105,7 +105,11 @@ class Module:
 
     @classmethod
     def validate(cls, value):
-        return import_string(value)
+        try:
+            return import_string(value)
+        except ImportError as e:
+            # errors must be TypeError or ValueError
+            raise ValueError(str(e)) from e
 
 
 class DSN(str):

tests/test_complex.py

@@ -18,7 +18,7 @@ def test_str_bytes():
     )
 
     m = StrBytesModel(v=b'b')
-    assert m.v == b'b'
+    assert m.v == 'b'
 
     with pytest.raises(ValidationError) as exc_info:
         StrBytesModel(v=None)
@@ -50,7 +50,7 @@ def test_str_bytes_none():
     assert m.v == 's'
 
     m = StrBytesModel(v=b'b')
-    assert m.v == b'b'
+    assert m.v == 'b'
 
     m = StrBytesModel(v=None)
     assert m.v is None
@@ -73,14 +73,14 @@ def test_union_int_str():
     assert m.v == 123
 
     m = Model(v='123')
-    assert m.v == '123'
+    assert m.v == 123
 
     m = Model(v=b'foobar')
     assert m.v == 'foobar'
 
     # here both validators work and it's impossible to work out which value "closer"
     m = Model(v=12.2)
-    assert m.v == '12.2'
+    assert m.v == 12
 
     with pytest.raises(ValidationError) as exc_info:
         Model(v=None)
@@ -104,6 +104,17 @@ def test_union_int_str():
 }""" == exc_info.value.json(2)
 
 
+def test_union_priority():
+    class ModelOne(BaseModel):
+        v: Union[int, str] = ...
+
+    class ModelTwo(BaseModel):
+        v: Union[str, int] = ...
+
+    assert ModelOne(v='123').v == 123
+    assert ModelTwo(v='123').v == '123'
+
+
 def test_typed_list():
     class Model(BaseModel):
         v: List[int] = ...

tests/test_types.py

@@ -76,6 +76,9 @@ class ModuleModel(BaseModel):
 def test_module_import():
     m = ModuleModel()
     assert m.module == os.path
+    with pytest.raises(ValidationError) as exc_info:
+        ModuleModel(module='foobar')
+    assert '"\\"foobar\\" doesn\'t look like a module path"' in exc_info.value.args[0]
 
 
 class CheckModel(BaseModel):