[Python-Dev] Is static typing still optional?

[Terry Reedy]

On 12/21/2017 4:22 AM, Eric V. Smith wrote:
> On 12/21/2017 1:46 AM, Chris Barker wrote:

>> I suggest that it be clear in the docs, and ideally in the PEP, that 
>> the dataclass decorator is using the *annotation" syntax, and that the 
>> the only relevant part it uses is that an annotation exists, but the 
>> value of the annotation is essentially (completely?) ignored. 
> 
> I think the PEP is very clear about this: "The dataclass decorator 
> examines the class to find fields. A field is defined as any variable 
> identified in __annotations__. That is, a variable that has a type 
> annotation. With two exceptions described below, none of the Data Class 
> machinery examines the type specified in the annotation."

This seems clear enough.  It could come after describing what a 
dataclass *is*.

> I agree the docs should also be clear about this.


>> So we should have examples like:
>>
>> @dataclass
>> class C:
>>      a: ...  # field with no default
>>      b: ... = 0 # filed with a default value
>>
>> Then maybe:
>>
>> @dataclass
>> class C:
>>      a: "the a parameter" # field with no default
>>      b: "another, different parameter" = 0.0 # field with a default
>>
>> Then the docs can go to say that if the user wants to specify a type 
>> for use with a static type checking pre-processor, they can do it like 
>> so:
>>
>> @dataclass
>> class C:
>>      a: int # integer field with no default
>>      b: float = 0.0 # float field with a default
>>
>> And the types will be recognized by type checkers such as mypy.
>>
>> And I think the non-typed examples should go first in the docs.

Module some bike-shedding, the above seems pretty good to me.
> 
> I'll leave this for others to decide. The docs, and how approachable 
> they are to various audiences, isn't my area of expertise.

-- 
Terry Jan Reedy