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bpo-46642: explicitly disallow typing.TypeVar instance subclassing by GBeauregard · Pull Request #31148 · python/cpython · GitHub

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bpo-46642: explicitly disallow typing.TypeVar instance subclassing #31148

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Merged
serhiy-storchaka merged 7 commits into from
Jun 25, 2022
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bpo-46642: explicitly disallow typing.TypeVar instance subclassing #31148

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c51f48e
explicitly disallow typing.TypeVar subclassing
GBeauregard Feb 5, 2022
3659772
📜🤖 Added by blurb_it.
blurb-it[bot] Feb 5, 2022
a3c54d5
make test match regex
GBeauregard Feb 6, 2022
3b68cda
Merge branch 'python:main' into fix-typevar-test
GBeauregard Feb 6, 2022
a7a6074
Merge branch 'main' into fix-typevar-test
serhiy-storchaka Jun 21, 2022
bf233d1
More explicit errors and more tests.
serhiy-storchaka Jun 21, 2022
a854d32
Update a NEWS entry.
serhiy-storchaka Jun 21, 2022
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107 changes: 68 additions & 39 deletions Lib/test/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -51,6 +51,10 @@
c_typing = import_helper.import_fresh_module('typing', fresh=['_typing'])


CANNOT_SUBCLASS_TYPE = 'Cannot subclass special typing classes'
CANNOT_SUBCLASS_INSTANCE = 'Cannot subclass an instance of %s'


class BaseTestCase(TestCase):

def assertIsSubclass(self, cls, class_or_tuple, msg=None):
Expand Down Expand Up @@ -170,10 +174,11 @@ def test_not_generic(self):
self.bottom_type[int]

def test_cannot_subclass(self):
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError,
'Cannot subclass ' + re.escape(str(self.bottom_type))):
class A(self.bottom_type):
pass
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class A(type(self.bottom_type)):
pass

Expand Down Expand Up @@ -266,10 +271,11 @@ def test_cannot_subscript(self):
Self[int]

def test_cannot_subclass(self):
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(type(Self)):
pass
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError,
r'Cannot subclass typing\.Self'):
class C(Self):
pass

Expand Down Expand Up @@ -322,10 +328,11 @@ def test_cannot_subscript(self):
LiteralString[int]

def test_cannot_subclass(self):
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(type(LiteralString)):
pass
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError,
r'Cannot subclass typing\.LiteralString'):
class C(LiteralString):
pass

Expand Down Expand Up @@ -415,15 +422,13 @@ def test_no_redefinition(self):
self.assertNotEqual(TypeVar('T'), TypeVar('T'))
self.assertNotEqual(TypeVar('T', int, str), TypeVar('T', int, str))

def test_cannot_subclass_vars(self):
with self.assertRaises(TypeError):
class V(TypeVar('T')):
pass

def test_cannot_subclass_var_itself(self):
with self.assertRaises(TypeError):
class V(TypeVar):
pass
def test_cannot_subclass(self):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class V(TypeVar): pass
T = TypeVar("T")
with self.assertRaisesRegex(TypeError,
CANNOT_SUBCLASS_INSTANCE % 'TypeVar'):
class V(T): pass

def test_cannot_instantiate_vars(self):
with self.assertRaises(TypeError):
Expand Down Expand Up @@ -1016,15 +1021,14 @@ class A(Generic[Unpack[Ts]]): pass
self.assertEndsWith(repr(F[float]), 'A[float, *tuple[str, ...]]')
self.assertEndsWith(repr(F[float, str]), 'A[float, str, *tuple[str, ...]]')

def test_cannot_subclass_class(self):
with self.assertRaises(TypeError):
def test_cannot_subclass(self):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(TypeVarTuple): pass

def test_cannot_subclass_instance(self):
Ts = TypeVarTuple('Ts')
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError,
CANNOT_SUBCLASS_INSTANCE % 'TypeVarTuple'):
class C(Ts): pass
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError, r'Cannot subclass \*Ts'):
class C(Unpack[Ts]): pass

def test_variadic_class_args_are_correct(self):
Expand Down Expand Up @@ -1411,13 +1415,15 @@ def test_repr(self):
self.assertEqual(repr(u), 'typing.Optional[str]')

def test_cannot_subclass(self):
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError,
r'Cannot subclass typing\.Union'):
class C(Union):
pass
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(type(Union)):
pass
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError,
r'Cannot subclass typing\.Union\[int, str\]'):
class C(Union[int, str]):
pass

Expand Down Expand Up @@ -3658,10 +3664,10 @@ def test_repr(self):
self.assertEqual(repr(cv), 'typing.ClassVar[%s.Employee]' % __name__)

def test_cannot_subclass(self):
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(type(ClassVar)):
pass
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(type(ClassVar[int])):
pass

Expand Down Expand Up @@ -3700,10 +3706,10 @@ def test_repr(self):
self.assertEqual(repr(cv), 'typing.Final[tuple[int]]')

def test_cannot_subclass(self):
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(type(Final)):
pass
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(type(Final[int])):
pass

Expand Down Expand Up @@ -6206,16 +6212,18 @@ def test_repr(self):
self.assertEqual(repr(cv), f'typing.Required[{__name__}.Employee]')

def test_cannot_subclass(self):
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(type(Required)):
pass
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(type(Required[int])):
pass
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError,
r'Cannot subclass typing\.Required'):
class C(Required):
pass
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError,
r'Cannot subclass typing\.Required\[int\]'):
class C(Required[int]):
pass

Expand Down Expand Up @@ -6252,16 +6260,18 @@ def test_repr(self):
self.assertEqual(repr(cv), f'typing.NotRequired[{__name__}.Employee]')

def test_cannot_subclass(self):
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(type(NotRequired)):
pass
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(type(NotRequired[int])):
pass
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError,
r'Cannot subclass typing\.NotRequired'):
class C(NotRequired):
pass
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError,
r'Cannot subclass typing\.NotRequired\[int\]'):
class C(NotRequired[int]):
pass

Expand Down Expand Up @@ -6677,7 +6687,8 @@ def test_no_issubclass(self):
issubclass(TypeAlias, Employee)

def test_cannot_subclass(self):
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError,
r'Cannot subclass typing\.TypeAlias'):
class C(TypeAlias):
pass

Expand Down Expand Up @@ -6879,6 +6890,24 @@ def test_paramspec_gets_copied(self):
self.assertEqual(C2[Concatenate[str, P2]].__parameters__, (P2,))
self.assertEqual(C2[Concatenate[T, P2]].__parameters__, (T, P2))

def test_cannot_subclass(self):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(ParamSpec): pass
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(ParamSpecArgs): pass
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(ParamSpecKwargs): pass
P = ParamSpec('P')
with self.assertRaisesRegex(TypeError,
CANNOT_SUBCLASS_INSTANCE % 'ParamSpec'):
class C(P): pass
with self.assertRaisesRegex(TypeError,
CANNOT_SUBCLASS_INSTANCE % 'ParamSpecArgs'):
class C(P.args): pass
with self.assertRaisesRegex(TypeError,
CANNOT_SUBCLASS_INSTANCE % 'ParamSpecKwargs'):
class C(P.kwargs): pass


class ConcatenateTests(BaseTestCase):
def test_basics(self):
Expand Down Expand Up @@ -6945,10 +6974,10 @@ def test_repr(self):
self.assertEqual(repr(cv), 'typing.TypeGuard[tuple[int]]')

def test_cannot_subclass(self):
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(type(TypeGuard)):
pass
with self.assertRaises(TypeError):
with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
class C(type(TypeGuard[int])):
pass

Expand Down
12 changes: 12 additions & 0 deletions Lib/typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -954,6 +954,9 @@ def __repr__(self):
prefix = '~'
return prefix + self.__name__

def __mro_entries__(self, bases):
raise TypeError(f"Cannot subclass an instance of {type(self).__name__}")


class TypeVar(_Final, _Immutable, _BoundVarianceMixin, _PickleUsingNameMixin,
_root=True):
Expand Down Expand Up @@ -1101,6 +1104,9 @@ def __typing_prepare_subst__(self, alias, args):
*args[alen - right:],
)

def __mro_entries__(self, bases):

serhiy-storchaka Mar 5, 2022

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

It should be added not here, but in _TypeVarLike. ParamSpec instances are not subclassable too.

serhiy-storchaka Mar 12, 2022

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

And add it also in TypeVarTuple.

GBeauregard Mar 18, 2022

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Thanks for the feedback! I'll get to this soon and ping you when done (I'm currently in the process of moving across the country and starting a job)
raise TypeError(f"Cannot subclass an instance of {type(self).__name__}")


class ParamSpecArgs(_Final, _Immutable, _root=True):
"""The args for a ParamSpec object.
Expand All @@ -1125,6 +1131,9 @@ def __eq__(self, other):
return NotImplemented
return self.__origin__ == other.__origin__

def __mro_entries__(self, bases):
raise TypeError(f"Cannot subclass an instance of {type(self).__name__}")


class ParamSpecKwargs(_Final, _Immutable, _root=True):
"""The kwargs for a ParamSpec object.
Expand All @@ -1149,6 +1158,9 @@ def __eq__(self, other):
return NotImplemented
return self.__origin__ == other.__origin__

def __mro_entries__(self, bases):
raise TypeError(f"Cannot subclass an instance of {type(self).__name__}")


class ParamSpec(_Final, _Immutable, _BoundVarianceMixin, _PickleUsingNameMixin,
_root=True):
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2022-02-05-18-46-54.bpo-46642.YI6nHQ.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Improve error message when trying to subclass an instance of :data:`typing.TypeVar`, :data:`typing.ParamSpec`, :data:`typing.TypeVarTuple`, etc. Based on patch by Gregory Beauregard.
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