Repository navigation
No error in function definition that returns unbound T #13061
Description
from typing import TypeVar
T = TypeVar('T')
def f() -> T: # no error
...
if f():
print() # Statement is unreachable
else:
print() # Statement is unreachableActual Behavior
No error in f definition. Two unreachable errors inside if f(): ... else: ...
Expected Behavior
Error in f definition. For example:
Type variable "T" is unbound
(Hint: Use "T" in function arguments to bind "T" to return type)
No errors inside if f(): ... else: ...
My Environment
mypy 0.961 (compiled: no)- no command-line flags, no config file
CPython 3.10.4- Windows 10
Activity
JukkaL commentedon Jul 16, 2022
Hints:
list[T]where the type variable is a component of some other type. Returninglist[T], for example, could be reasonable.TypeVarTypebut the return type is not present as a component in function argument types, generate an error.TypeTraverserVisitorto traverse the argument types, and overridevisit_type_varto collect all the references to type variables within a type. SeeCollectAllInstancesQueryfor an example of doing a similar thing.odesenfans commentedon Jul 16, 2022
Could you elaborate on why and when types like
list[T]could be acceptable ifTis not bound to any type?JukkaL commentedon Jul 16, 2022
@odesenfans The only example that I can think of is creating an empty container. For example, something like this:
Usually you would just call the type object, but having a factory function seems like a plausible use case (e.g. we could do some extra things like logging or collect statistics in the factory function).
Add unbound typevar check (#13166)
ilevkivskyi commentedon Sep 25, 2022
I think this was already fixed by #13166, but accidentally was not closed.