Improve error message for an invalid callable type #4213
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elazarg
reviewed
Nov 6, 2017
test-data/unit/check-generics.test
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| @@ -812,7 +812,7 @@ class Node(Generic[T]): | |||
| def __init__(self, x: T) -> None: | |||
| ... | |||
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| BadC = Callable[T] # E: Invalid function type | |||
| BadC = Callable[T] # E: Callable takes 0 or 2 arguments, not 1 | |||
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This error is ambiguous, since it looks like it is about the callable itself, not the the type-constructor "Callable". At least quote it: "Callable" takes 0 or 2 arguments, not 1.
Additionally, I think it's better not to talk about "number of arguments" - again, can be confused with function arguments. Instead it might be more obvious if the message demonstrated the two possibilities. Something like Please use "Callable[[<parameters>], <return type>].
What is the "0 arguments" case? The ... form?
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I guess the "0 arguments" case is plain Callable with omitted arguments. I agree with you that the message is confusing.
If the user gives the wrong number of arguments to Callable[], tell them how many arguments are expected.
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JukkaL
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Nov 15, 2017
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If the user gives the wrong number of arguments to Callable[], tell them
how many arguments are expected.