Improve message if user forgot to call a function

Forgetting to call a method, i.e. missing (), is a somewhat common programming error. Mypy will typically catch this error, but often error messages includes something like "Callable[...]" has no attribute "foo". Since the callable type may be pretty complicated, this can look confusing.

Here are a few ideas that could make this better:

1. Only say Callable object has no attribute "foo" (omit the full callable type).
2. Add a note such as Did you mean ".foo()" (with parentheses)? (needs wordsmithing).
3. In addition to (1), show the signature of the function in a separate note pretty-printed using function definition syntax such as def foo() -> List[X].

No se nombra ningún archivo ni prueba. Empieza por localizar la ruta de diagnóstico de mypy para un objeto Callable del que se informa que carece de un atributo y, después, compara las opciones propuestas de redacción y de nota de signatura. Se considera hecho cuando el tipo Callable confuso se presenta con mayor claridad y la cobertura de regresión verifica la indicación sobre los paréntesis que faltan.