Checks in tests/typing intended to be exact matches should be done with assert_type instead of simply assigning to variables
Explanation
Consider the following functions
def f_any() -> Any:
return ...
def f_int() -> int:
return 1Assigning to vars to check
# It might look like we're asserting the return type of function is Any
var1: Any = f_any()
# But all it does it asserting that return_any() is assignable to Any
# which is always true for any functions
var2: Any = f_int() # This is ok with mypy
Using assert_type
assert_type(f_any(), Any)
assert_type(f_int(), Any) # error: Expression is of type "int", not "Any" [assert-type]
The usecase for simply assigning to variables is to check if a variable is a subclass (or "assignable" to be specific) of a specific type. For example.
var1: Animal = f_cat() # We don't care if the stub declares f_cat to return Animal or Cat
But in the usecase of stub-testing, we probably almost always want to check exact type insteaad of assignability.
Examples
Example 1:
This will pass regardless of the return type of provider1
Example 2:
|
animal10: Animal = factory10() |
The example is supposed to check if explicitly typing factory10: Provider.Animal makes factory10() return Animal instead of Cat.
But it doesn't check that, since Cat is assignable to Animal, which defeats the purpose of the test
factory10 = providers.Factory(Cat)
animal10: Animal = factory10() # Here will still pass even though it returns cat
This, on the other hand, will work as intended
factory10: providers.Provider[Animal] = providers.Factory(Cat)
assert_type(factory10(), Animal)
There are probably a lot more examples
Checks in
tests/typingintended to be exact matches should be done withassert_typeinstead of simply assigning to variablesExplanation
Consider the following functions
Assigning to vars to check
Using assert_type
The usecase for simply assigning to variables is to check if a variable is a subclass (or "assignable" to be specific) of a specific type. For example.
But in the usecase of stub-testing, we probably almost always want to check exact type insteaad of assignability.
Examples
Example 1:
python-dependency-injector/tests/typing/selector.py
Line 11 in 5a1aef9
This will pass regardless of the return type of
provider1Example 2:
python-dependency-injector/tests/typing/factory.py
Line 92 in 5a1aef9
The example is supposed to check if explicitly typing
factory10: Provider.Animalmakesfactory10()returnAnimalinstead ofCat.But it doesn't check that, since
Catis assignable toAnimal, which defeats the purpose of the testThis, on the other hand, will work as intended
There are probably a lot more examples