Sorry, Matt: I meant to credit you by name, but forgot to during my
final edit.
I still don't like the verbosity and the look of 'with' statements or
classes. Or the fact that some of the fields are indented relative to
others.
And should also mention that Ethan Furman suggested using '*' and '/' as
the "type", in
https://mail.python.org/archives/list/python-ideas@python.org/message/BIAVX4O6JRPQY7S3XG2IX6BSBZLAR2NS/
, although the interaction with typing (specifically get_type_hints)
might be an issue:
class Hmm:
#
this: int
that: float
#
pos: '/'
#
these: str
those: str
#
key: '*'
#
some: list
Anyway, Matt's and Ethan's proposal are on the other thread. I'd like to
keep this thread focused on my proposal of dataclasses.KW_ONLY and
.POS_ONLY. Not that saying "I'd like focus this thread" has ever worked
in the history of python-ideas.
Eric
On 3/13/2021 2:40 AM, Matt Wozniski wrote:
On Fri, Mar 12, 2021, 11:55 PM Eric V. Smith <e...@trueblade.com
<mailto:e...@trueblade.com>> wrote:
I should mention another idea that showed up on python-ideas, at
https://mail.python.org/archives/list/python-ideas@python.org/message/WBL4X46QG2HY5ZQWYVX4MXG5LK7QXBWB/
<https://mail.python.org/archives/list/python-ideas@python.org/message/WBL4X46QG2HY5ZQWYVX4MXG5LK7QXBWB/>
. It would allow you to specify the flag via code like:
@dataclasses.dataclass
class Parent:
with dataclasses.positional():
a: int
c: bool = False
with dataclasses.keyword():
e: list
I'm not crazy about it, and it looks like it would require stack
inspection to get it to work, but I mention it here for completeness.
I think stack inspection could be avoided if we did something like:
```
@dataclasses.dataclass
class Parent:
class pos(dataclasses.PositionalOnly):
a: int
c: bool = False
class kw(dataclasses.KeywordOnly):
e: list
```
Like your proposal, the names for the two inner classes can be
anything, but they must be unique. The metaclass would check if a
field in the new class's namespace was a subclass of PositionalOnly or
KeywordOnly, and if so recurse into its annotations to collect more
fields.
This still seems hacky, but it seems to read reasonably nicely, and
behaves obviously in the presence of subclassing.
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Eric V. Smith
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