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Make Mapping covariant in keys (too). #273

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Make Mapping covariant in keys (too). #273

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10 changes: 5 additions & 5 deletions python2/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -838,15 +838,15 @@ def test_covariance_sequence(self):
typing.Sequence[Manager])

def test_covariance_mapping(self):
# Ditto for Mapping (covariant in the value, invariant in the key).
# Ditto for Mapping (covariant in key and value).
self.assertIsSubclass(typing.Mapping[Employee, Manager],
typing.Mapping[Employee, Employee])
self.assertNotIsSubclass(typing.Mapping[Manager, Employee],
typing.Mapping[Employee, Employee])
self.assertIsSubclass(typing.Mapping[Manager, Employee],
typing.Mapping[Employee, Employee])
self.assertNotIsSubclass(typing.Mapping[Employee, Manager],
typing.Mapping[Manager, Manager])
typing.Mapping[Manager, Manager])
self.assertNotIsSubclass(typing.Mapping[Manager, Employee],
typing.Mapping[Manager, Manager])
typing.Mapping[Manager, Manager])


class CastTests(BaseTestCase):
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7 changes: 5 additions & 2 deletions python2/typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -459,6 +459,7 @@ def __subclasscheck__(self, cls):
VT = TypeVar('VT') # Value type.
T_co = TypeVar('T_co', covariant=True) # Any type covariant containers.
V_co = TypeVar('V_co', covariant=True) # Any type covariant containers.
KT_co = TypeVar('KT', covariant=True) # Key type covariant containers.
VT_co = TypeVar('VT_co', covariant=True) # Value type covariant containers.
T_contra = TypeVar('T_contra', contravariant=True) # Ditto contravariant.

Expand Down Expand Up @@ -1391,8 +1392,10 @@ class MutableSet(AbstractSet[T]):
__extra__ = collections_abc.MutableSet


# NOTE: It is only covariant in the value type.
class Mapping(Sized, Iterable[KT], Container[KT], Generic[KT, VT_co]):
# NOTE: Covariance in the key type is theoretically problematic because
# there are methods with KT parameters, but in this case it's okay.
# See https://github.com/python/typeshed/issues/510.
class Mapping(Sized, Iterable[KT_co], Container[KT_co], Generic[KT_co, VT_co]):
__extra__ = collections_abc.Mapping


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10 changes: 5 additions & 5 deletions src/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -863,15 +863,15 @@ def test_covariance_sequence(self):
typing.Sequence[Manager])

def test_covariance_mapping(self):
# Ditto for Mapping (covariant in the value, invariant in the key).
# Ditto for Mapping (covariant in key and value).
self.assertIsSubclass(typing.Mapping[Employee, Manager],
typing.Mapping[Employee, Employee])
self.assertNotIsSubclass(typing.Mapping[Manager, Employee],
typing.Mapping[Employee, Employee])
self.assertIsSubclass(typing.Mapping[Manager, Employee],
typing.Mapping[Employee, Employee])
self.assertNotIsSubclass(typing.Mapping[Employee, Manager],
typing.Mapping[Manager, Manager])
typing.Mapping[Manager, Manager])
self.assertNotIsSubclass(typing.Mapping[Manager, Employee],
typing.Mapping[Manager, Manager])
typing.Mapping[Manager, Manager])


class CastTests(BaseTestCase):
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9 changes: 6 additions & 3 deletions src/typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -452,6 +452,7 @@ def __subclasscheck__(self, cls):
VT = TypeVar('VT') # Value type.
T_co = TypeVar('T_co', covariant=True) # Any type covariant containers.
V_co = TypeVar('V_co', covariant=True) # Any type covariant containers.
KT_co = TypeVar('KT', covariant=True) # Key type covariant containers.
VT_co = TypeVar('VT_co', covariant=True) # Value type covariant containers.
T_contra = TypeVar('T_contra', contravariant=True) # Ditto contravariant.

Expand Down Expand Up @@ -1454,13 +1455,15 @@ class MutableSet(AbstractSet[T], extra=collections_abc.MutableSet):
pass


# NOTE: It is only covariant in the value type.
# NOTE: Covariance in the key type is theoretically problematic because
# there are methods with KT parameters, but in this case it's okay.
# See https://github.com/python/typeshed/issues/510.
if hasattr(collections_abc, 'Collection'):
class Mapping(Collection[KT], Generic[KT, VT_co],
class Mapping(Collection[KT_co], Generic[KT_co, VT_co],
extra=collections_abc.Mapping):
pass
else:
class Mapping(Sized, Iterable[KT], Container[KT], Generic[KT, VT_co],
class Mapping(Sized, Iterable[KT_co], Container[KT_co], Generic[KT_co, VT_co],
extra=collections_abc.Mapping):
pass

Expand Down