On 12/21/2017 7:55 PM, MRAB wrote:
On 2017-12-22 00:19, Gregory P. Smith wrote:
(subject for this sub-thread updated)
On Thu, Dec 21, 2017 at 4:08 PM Chris Barker <chris.bar...@noaa.gov
<mailto:chris.bar...@noaa.gov>> wrote:
On Thu, Dec 21, 2017 at 3:36 PM, Gregory P. Smith <g...@krypto.org
<mailto:g...@krypto.org>> wrote:
But we already have ... which does - so I'd suggest that for
people who are averse to importing anything from typing and
using the also quite readable Any. (ie: document this as the
expected practice with both having the same meaning)
I don't think they do, actually - I haven't been following the
typing discussions, but someone in this thread said that ... means
"use the type of teh default" or something like that.
indeed, they may not. though if that is the definition is it
reasonable to say that type analyzers recognize the potential
recursive meaning when the _default_ is ... and treat that as Any?
another option that crossed my mind was "a: 10" without using =. but
that really abuses __attributes__ by sticking the default value in
there which the @dataclass decorator would presumably immediately need
to undo and fix up before returning the class. but I don't find
assigning a value without an = sign to be pythonic so please lets not
do that! :)
If you allowed "a: 10" (an int value), then you might also allow "a:
'foo'" (a string value), but wouldn't that be interpreted as a type
called "foo"?
As far as dataclasses are concerned, both of these are allowed, and
since neither is ClassVar or InitvVar, they're ignored. Type checkers
would object to the int, and I assume also the string unless there was a
type foo defined. See
https://www.python.org/dev/peps/pep-0484/#the-problem-of-forward-declarations
and typing.get_type_hints().
It's a bug that dataclasses currently does not inspect string
annotations to see if they're actually ClassVar or InitVar declarations.
PEP 563 makes it critical (and not merely important) to look at the
string annotations. Whether or not that involves typing.get_type_hints()
or not, I haven't yet decided. I'm waiting for PEPs 563 and 560 to be
implemented before taking another look at it.
Eric.
If you can't have a string value, then you shouldn't have an int value
either.
[snip]
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