Repository navigation
Weird error messages when mixing classes with instances #3050
Description
class A: pass
x: Tuple[A]
x = A, # E: Incompatible types in assignment (expression has type "Tuple[A]", variable has type "Tuple[A]")
y: Tuple[Type[A]]
y = A, # OK, expected
def f(x: Tuple[A]) -> None: return None
f((A,)) # E: Argument 1 to "f" has incompatible type "Tuple[A]"; expected "Tuple[A]"
reveal_type((A,)) # E: Revealed type is 'Tuple[def () -> x.A]'
z: A
z = A # E: Incompatible types in assignment (expression has type "A" (type object), variable has type "A")
z = A, # E: Incompatible types in assignment (expression has type "Tuple[A]", variable has type "A")Looks like mypy formats class type in three ways: T (which is wrong), T (type object), and def () -> T. In some cases these errors are unclear.
Activity
ilevkivskyi commentedon Mar 23, 2017
Yes, I remember I noticed this around a year ago, last two formats are OK I think, but the first one is definitely misleading.
ambv commentedon Apr 12, 2017
So the correct error message should be:
elazarg commentedon May 16, 2017
Example from #3372:
elazarg commentedon May 16, 2017
I will submit a PR is there is agreement on the correct error message is.
I am +1 on
Type[A]as @ambv suggested.elazarg commentedon May 16, 2017
I think the issue becomes even more confusing when dealing with metaclasses.
ilevkivskyi commentedon May 16, 2017
I am also +1 on
Type[A].gvanrossum commentedon May 16, 2017
Yup