New submission from Eric V. Smith <e...@trueblade.com>:
I've had several requests for keyword-only arguments. This is a placeholder to
remind me to work on it. I have not decided if it's a good idea or not.
I propose adding a keyword_only argument to field(), defaulting to False.
I'm thinking that the basic idea would be to put all keyword-only fields at the
end of the arguments to __init__, but for all other uses, leave them where they
appear in the class definition. That way comparison operations, in particular,
would use the fields as they appear in the class definition (which is the
current behavior). Since they'd be at the end of __init__, and since order
doesn't matter (they're keyword-only, after all), then this would work as
expected for base classes.
That is, given:
@dataclass
class B:
a: field(type=int, keyword_only=True)
b: int
@dataclass
class C(B):
c: int
d: field(type=int, keyword_only=True)
Then B's __init__ would take (b, c, *, a, d) as its arguments, but its
comparison functions would compare the tuples as (a, b, c, d).
It would be an error for a ClassVar field to be keyword-only. I think it would
be okay if an InitVar field were keyword-only, but I haven't given it a lot of
thought.
----------
assignee: eric.smith
components: Library (Lib)
messages: 316498
nosy: eric.smith
priority: normal
severity: normal
status: open
title: dataclasses: allow keyword-only arguments
type: enhancement
versions: Python 3.8
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue33493>
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