[Python-Dev] Is static typing still optional?

[David Mertz]

On Sun, Dec 17, 2017 at 8:22 AM, Guido van Rossum <guido at python.org> wrote:

> On Sun, Dec 17, 2017 at 2:11 AM, Julien Salort <listes at salort.eu> wrote:
>
>> Naive question from a lurker: does it mean that it works also if one
>> annotates with something that is not a type, e.g. a comment,
>>
>> @dataclass
>> class C:
>>     a: "This represents the amplitude" = 0.0
>>     b: "This is an offset" = 0.0
>
>
> I would personally not use the notation for this, but it is legal code.
> However static type checkers like mypy won't be happy with this.
>

Mypy definitely won't like that use of annotation, but documentation
systems might.  For example, in a hover tooltip in an IDE/editor, it's
probably more helpful to see the descriptive message than "int" or "float"
for the attribute.

What about data that isn't built-in scalars? Does this look right to people
(and will mypy be happy with it)?

@dataclass
class C:
    a:numpy.ndarray = numpy.random.random((3,3))
    b:MyCustomClass = MyCustomClass("foo", 37.2, 1+2j)

I don't think those look terrible, but I think this looks better:

@dataclass
class C:
    a:Infer = np.random.random((3,3))
    b:Infer = MyCustomClass("foo", 37.2, 1+2j)

Where the name 'Infer' (or some other spelling) was a name defined in the
`dataclasses` module.  In this case, I don't want to use `typing.Any` since
I really do want "the type of thing the default value has."

-- 
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