Wrapping class with icontract invariant decorator causes PyLance to incorrectly detect type. #1667
Comments
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This looks like it's a bug in the type annotations within the The decorator def __call__(self, cls: type) -> type:The correct type annotation for this method is: def __call__(self, cls: _T) -> _T:where `_T is defined as: _T = TypeVar("_T", bound=type)This preserves the type of the decorated class. If I make this change, it type checks fine in pylance and in mypy. I recommend filing a bug or submitting a PR in the |
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I worked with the developer behind icontract and he and I verified a fix on his side is possible (see his pull request #227). I still question why Python itself plus mypy had no issue with the looser typing but PyLance did. Either way, this may be solved by a change in PyLance. |
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Python doesn't care about annotations at runtime, so you could put anything there and it will run. As for mypy, that's hard to say. It could be a bug they haven't fixed or had reported to them. |
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This appears to be a bug in mypy. They are not honoring the |
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It looks like this is a known bug in mypy. It has been open for more than four years: python/mypy#3135. Here's an sample that demonstrates how pyright (the type checker that underlies pylance) applies the class decorator whereas mypy does not. from typing import Callable, TYPE_CHECKING, Type
class replace_with_int1:
def __init__(self):
...
def __call__(self, cls: type) -> Type[int]:
return int
@replace_with_int1()
class NotInt1:
...
if TYPE_CHECKING:
reveal_type(NotInt1) # pyright: "Type[int]"", mypy: "def () -> NotInt1"
print(NotInt1) # <class 'int'>
def replace_with_int2() -> Callable[..., Type[int]]:
return lambda x: int
@replace_with_int2()
class NotInt2:
...
if TYPE_CHECKING:
reveal_type(NotInt2) # pyright: "Type[int]"", mypy: "def () -> NotInt2"
print(NotInt2) # <class 'int'> |
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I'm going to close this as needing a fix upstream; we're doing the right thing according to the type annotations here, so there's no work to do. |
Environment data
Expected behaviour
When using icontract to add an invariant to a class, both mypy and Python's own type() command show the type of a class wrapped by icontract to be the same as one that was never wrapped. PyLance shouldn't have an issue with using a wrapped class in place of the bare class for type hinting.
Actual behaviour
TestClass1 is a bare class.
TestClass2 is a wrapped class.
(see below for the actual code)
PyLance states that TestClass1 is of type "Type[TestClass1]" while it shows that TestClass2 is of type "type".
PyLance states that TestClass2 can't be used to type annotate a dataclass field because it expected a Class but got a type instead. Further, because of that issue, PyLance states that variables within TestClass2 are of unknown type and can't be referenced. The code works fine.
Mypy states:
..and printing the type of each from Python shows:
Logs
Python Language Server Log
Code Snippet / Additional information
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