Re: [Python-Dev] Adding Type[C] to PEP 484
On Sat, May 14, 2016 at 11:47 AM, Peter Ludemann
wrote:
> I think that Type[C,D] would mean Union[Type[C], Type[D]], but I'm not
> sure ... I should probably talk to a typing expert about this.
> (Sorry for thinking out loud; but if we decide that Type[C,D] doesn't make
> sense, we need to prohibit it)
>
It sounds iffy enough to prohibit.
> I suppose I'm asking: do we allow new_user(Type[BasicUser, ProUser])?
>
That looks like a call, but Type[] is something to use in the definition.
> Here's a trivial example that off the top of my head makes sense:
>
> BasicOrProUser = TypeVar('BasicOrProUser', BasicUser, ProUser)
> def new_user(name: str, user_factory: Type[BasicOrProuser]) ->
> BasicOrProUser:
> return user_factory(name)
>
That looks reasonable and only has one parameter to Type[].
> Or must the Type[...] item have been defined with a TypeVar(...,
> bound=...), in which case multiple types aren't allowed with Type[...]?
>
You can use whatever you want. If you want to write Type[int] go right
ahead. Even Type[Union[int, str]] should be allowed. There is *usually* a
good reason to use a type variable though -- without one the return type
would be the base class. (But then again maybe that could be what you want,
or you might not even have a return type, e.g. when the thing just gets
thrown into the database.)
--Guido
>
>
> On 14 May 2016 at 11:30, Guido van Rossum wrote:
>
>> What would Type[C, D] mean?
>>
>> --Guido (mobile)
>> On May 14, 2016 11:21 AM, "Peter Ludemann via Python-Dev" <
>> python-dev@python.org> wrote:
>>
>>> Is Type[C,D] allowed? Or should multiple types be restricted to TypeVar?
>>>
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Re: [Python-Dev] Adding Type[C] to PEP 484
I think that Type[C,D] would mean Union[Type[C], Type[D]], but I'm not sure
... I should probably talk to a typing expert about this.
(Sorry for thinking out loud; but if we decide that Type[C,D] doesn't make
sense, we need to prohibit it)
I suppose I'm asking: do we allow new_user(Type[BasicUser, ProUser])?
Here's a trivial example that off the top of my head makes sense:
BasicOrProUser = TypeVar('BasicOrProUser', BasicUser, ProUser)
def new_user(name: str, user_factory: Type[BasicOrProuser]) ->
BasicOrProUser:
return user_factory(name)
Or must the Type[...] item have been defined with a TypeVar(...,
bound=...), in which case multiple types aren't allowed with Type[...]?
On 14 May 2016 at 11:30, Guido van Rossum wrote:
> What would Type[C, D] mean?
>
> --Guido (mobile)
> On May 14, 2016 11:21 AM, "Peter Ludemann via Python-Dev" <
> python-dev@python.org> wrote:
>
>> Is Type[C,D] allowed? Or should multiple types be restricted to TypeVar?
>>
>> ___
>> Python-Dev mailing list
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>> https://mail.python.org/mailman/listinfo/python-dev
>> Unsubscribe:
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>>
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Re: [Python-Dev] Adding Type[C] to PEP 484
What would Type[C, D] mean? --Guido (mobile) On May 14, 2016 11:21 AM, "Peter Ludemann via Python-Dev" < python-dev@python.org> wrote: > Is Type[C,D] allowed? Or should multiple types be restricted to TypeVar? > > ___ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > https://mail.python.org/mailman/options/python-dev/guido%40python.org > > ___ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Adding Type[C] to PEP 484
Is Type[C,D] allowed? Or should multiple types be restricted to TypeVar? ___ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] file system path protocol PEP
On 14 May 2016 at 19:36, Sven R. Kunze wrote: > Fine example. Thinking naively, I would say, when somebody made an effort to > write __fspath__, it should be respected. Maybe, that's just me. Over time, we've generally moved towards treating subclasses as if they were the base class where protocols are concerned, and encouraging the use of composition if people don't actually want that "is-a" behaviour. For example, compare the int protocol to the last major type protocol we added, index: >>> from operator import index >>> class MyInt(int): ... def __int__(self): ... return 42 ... def __index__(self): ... return 42 ... >>> x = MyInt(5) >>> x 5 >>> int(x) 42 >>> index(x) 5 In the case of retroactively added protocols like operator.index() and os.fspath(), where inheritance from the relevant builtin type was previously the only option, retaining that behaviour is also the only way to avoid a performance regression for those subclasses. Cheers, Nick. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia ___ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] file system path protocol PEP
On 13.05.2016 18:43, Chris Angelico wrote:
https://docs.python.org/3/c-api/unicode.html#c.PyUnicode_Check
https://docs.python.org/3/c-api/unicode.html#c.PyUnicode_CheckExact
Thanks for pointing me at this.
I searched via github and found usages only:
https://github.com/python/cpython/search?utf8=%E2%9C%93&q=PyUnicode_Check
"Check" accepts subclasses; "CheckExact" doesn't (it's like "type(x)
is str"). The question is, which one SHOULD be being done? What should
this do:
class TmpPath(str):
def __fspath__(self):
return "/tmp/"+self
x = TmpPath("foo/bar")
open(x, "w")
Does that respect __fspath__, or respect the fact that it's a string?
Fine example. Thinking naively, I would say, when somebody made an
effort to write __fspath__, it should be respected. Maybe, that's just me.
Not sure if that can be a source of errors, when somebody adds str as
baseclass later because the team needs str functionality. At least I
would expect __fspath__ to still work .
Best,
Sven
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