[Python-Dev] Is static typing still optional? (original) (raw)

Terry Reedy tjreedy at udel.edu
Thu Dec 21 05:22:27 EST 2017

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

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