Weird error messages when mixing classes with instances

[miedzinski]

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.

[ilevkivskyi]

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]

So the correct error message should be:

E: Incompatible types in assignment (expression has type "Tuple[Type[A]]", variable has type "Tuple[A]")

[elazarg]

Example from #3372:

class A: pass
class B(A): pass
def f(a: A): pass

f(B)  # E: Argument 1 to "f" has incompatible type "B"; expected "A"
a: A = B  # E: Incompatible types in assignment (expression has type "B", variable has type "A")

[elazarg]

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]

I think the issue becomes even more confusing when dealing with metaclasses.

[ilevkivskyi]

I am also +1 on Type[A].

[gvanrossum]

Yup