diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py index 7a725dfb520..eaaed63ef28 100644 --- a/Lib/dataclasses.py +++ b/Lib/dataclasses.py @@ -8,6 +8,7 @@ __all__ = ['dataclass', 'field', 'FrozenInstanceError', 'InitVar', + 'MISSING', # Helper functions. 'fields', @@ -29,11 +30,11 @@ class _HAS_DEFAULT_FACTORY_CLASS: return '' _HAS_DEFAULT_FACTORY = _HAS_DEFAULT_FACTORY_CLASS() -# A sentinel object to detect if a parameter is supplied or not. -class _MISSING_FACTORY: - def __repr__(self): - return '' -_MISSING = _MISSING_FACTORY() +# A sentinel object to detect if a parameter is supplied or not. Use +# a class to give it a better repr. +class _MISSING_TYPE: + pass +MISSING = _MISSING_TYPE() # Since most per-field metadata will be unused, create an empty # read-only proxy that can be shared among all fields. @@ -114,7 +115,7 @@ class Field: # This function is used instead of exposing Field creation directly, # so that a type checker can be told (via overloads) that this is a # function whose type depends on its parameters. -def field(*, default=_MISSING, default_factory=_MISSING, init=True, repr=True, +def field(*, default=MISSING, default_factory=MISSING, init=True, repr=True, hash=None, compare=True, metadata=None): """Return an object to identify dataclass fields. @@ -130,7 +131,7 @@ def field(*, default=_MISSING, default_factory=_MISSING, init=True, repr=True, It is an error to specify both default and default_factory. """ - if default is not _MISSING and default_factory is not _MISSING: + if default is not MISSING and default_factory is not MISSING: raise ValueError('cannot specify both default and default_factory') return Field(default, default_factory, init, repr, hash, compare, metadata) @@ -149,12 +150,12 @@ def _tuple_str(obj_name, fields): def _create_fn(name, args, body, globals=None, locals=None, - return_type=_MISSING): + return_type=MISSING): # Note that we mutate locals when exec() is called. Caller beware! if locals is None: locals = {} return_annotation = '' - if return_type is not _MISSING: + if return_type is not MISSING: locals['_return_type'] = return_type return_annotation = '->_return_type' args = ','.join(args) @@ -182,7 +183,7 @@ def _field_init(f, frozen, globals, self_name): # initialize this field. default_name = f'_dflt_{f.name}' - if f.default_factory is not _MISSING: + if f.default_factory is not MISSING: if f.init: # This field has a default factory. If a parameter is # given, use it. If not, call the factory. @@ -210,10 +211,10 @@ def _field_init(f, frozen, globals, self_name): else: # No default factory. if f.init: - if f.default is _MISSING: + if f.default is MISSING: # There's no default, just do an assignment. value = f.name - elif f.default is not _MISSING: + elif f.default is not MISSING: globals[default_name] = f.default value = f.name else: @@ -236,14 +237,14 @@ def _init_param(f): # For example, the equivalent of 'x:int=3' (except instead of 'int', # reference a variable set to int, and instead of '3', reference a # variable set to 3). - if f.default is _MISSING and f.default_factory is _MISSING: + if f.default is MISSING and f.default_factory is MISSING: # There's no default, and no default_factory, just # output the variable name and type. default = '' - elif f.default is not _MISSING: + elif f.default is not MISSING: # There's a default, this will be the name that's used to look it up. default = f'=_dflt_{f.name}' - elif f.default_factory is not _MISSING: + elif f.default_factory is not MISSING: # There's a factory function. Set a marker. default = '=_HAS_DEFAULT_FACTORY' return f'{f.name}:_type_{f.name}{default}' @@ -261,13 +262,13 @@ def _init_fn(fields, frozen, has_post_init, self_name): for f in fields: # Only consider fields in the __init__ call. if f.init: - if not (f.default is _MISSING and f.default_factory is _MISSING): + if not (f.default is MISSING and f.default_factory is MISSING): seen_default = True elif seen_default: raise TypeError(f'non-default argument {f.name!r} ' 'follows default argument') - globals = {'_MISSING': _MISSING, + globals = {'MISSING': MISSING, '_HAS_DEFAULT_FACTORY': _HAS_DEFAULT_FACTORY} body_lines = [] @@ -368,7 +369,7 @@ def _get_field(cls, a_name, a_type): # If the default value isn't derived from field, then it's # only a normal default value. Convert it to a Field(). - default = getattr(cls, a_name, _MISSING) + default = getattr(cls, a_name, MISSING) if isinstance(default, Field): f = default else: @@ -404,7 +405,7 @@ def _get_field(cls, a_name, a_type): # Special restrictions for ClassVar and InitVar. if f._field_type in (_FIELD_CLASSVAR, _FIELD_INITVAR): - if f.default_factory is not _MISSING: + if f.default_factory is not MISSING: raise TypeError(f'field {f.name} cannot have a ' 'default factory') # Should I check for other field settings? default_factory @@ -474,7 +475,7 @@ def _process_class(cls, repr, eq, order, hash, init, frozen): # with the real default. This is so that normal class # introspection sees a real default value, not a Field. if isinstance(getattr(cls, f.name, None), Field): - if f.default is _MISSING: + if f.default is MISSING: # If there's no default, delete the class attribute. # This happens if we specify field(repr=False), for # example (that is, we specified a field object, but diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py index 7fbea76ccd8..ed695639882 100755 --- a/Lib/test/test_dataclasses.py +++ b/Lib/test/test_dataclasses.py @@ -1,6 +1,6 @@ from dataclasses import ( dataclass, field, FrozenInstanceError, fields, asdict, astuple, - make_dataclass, replace, InitVar, Field + make_dataclass, replace, InitVar, Field, MISSING ) import pickle @@ -917,12 +917,12 @@ class TestCase(unittest.TestCase): param = next(params) self.assertEqual(param.name, 'k') self.assertIs (param.annotation, F) - # Don't test for the default, since it's set to _MISSING + # Don't test for the default, since it's set to MISSING self.assertEqual(param.kind, inspect.Parameter.POSITIONAL_OR_KEYWORD) param = next(params) self.assertEqual(param.name, 'l') self.assertIs (param.annotation, float) - # Don't test for the default, since it's set to _MISSING + # Don't test for the default, since it's set to MISSING self.assertEqual(param.kind, inspect.Parameter.POSITIONAL_OR_KEYWORD) self.assertRaises(StopIteration, next, params) @@ -948,6 +948,52 @@ class TestCase(unittest.TestCase): validate_class(C) + def test_missing_default(self): + # Test that MISSING works the same as a default not being + # specified. + @dataclass + class C: + x: int=field(default=MISSING) + with self.assertRaisesRegex(TypeError, + r'__init__\(\) missing 1 required ' + 'positional argument'): + C() + self.assertNotIn('x', C.__dict__) + + @dataclass + class D: + x: int + with self.assertRaisesRegex(TypeError, + r'__init__\(\) missing 1 required ' + 'positional argument'): + D() + self.assertNotIn('x', D.__dict__) + + def test_missing_default_factory(self): + # Test that MISSING works the same as a default factory not + # being specified (which is really the same as a default not + # being specified, too). + @dataclass + class C: + x: int=field(default_factory=MISSING) + with self.assertRaisesRegex(TypeError, + r'__init__\(\) missing 1 required ' + 'positional argument'): + C() + self.assertNotIn('x', C.__dict__) + + @dataclass + class D: + x: int=field(default=MISSING, default_factory=MISSING) + with self.assertRaisesRegex(TypeError, + r'__init__\(\) missing 1 required ' + 'positional argument'): + D() + self.assertNotIn('x', D.__dict__) + + def test_missing_repr(self): + self.assertIn('MISSING_TYPE object', repr(MISSING)) + def test_dont_include_other_annotations(self): @dataclass class C: