[Python-ideas] Type Hinting Kick-off

[Andrew Svetlov]

Sorry, I want to ask again.
The proposal is for static checks only?
My expectations for processing annotations in runtime as-is (just a
mark without any restrictions) will not changed?

On Sun, Dec 21, 2014 at 10:11 PM, Brett Cannon <brett at python.org> wrote:
> You're workflow won't necessarily break. You need to use a tool which
> expects type hints for function annotations to cause you any problems. If
> you simply don't use such a tool then you will have no problems.
>
>
> On Sun, Dec 21, 2014, 11:55 Andrew Svetlov <andrew.svetlov at gmail.com> wrote:
>>
>> The silly question.
>>
>> I use python 3 annotations for argument checking.
>>
>> My assumption is very simple, for
>>
>> def f(arg: checker): pass
>>
>> the checker will raise ValueError or TypeError if arg is not correct.
>> I do it by `checker(arg)` call.
>>
>> I use this in aiozmq rpc
>> (http://aiozmq.readthedocs.org/en/0.5/rpc.html#signature-validation)
>> for example and checkers from trafaret
>> (https://github.com/Deepwalker/trafaret) works fine.
>>
>> Will proposed change break my workflow?
>>
>> On Sun, Dec 21, 2014 at 6:53 PM, Guido van Rossum <guido at python.org>
>> wrote:
>> > On Sat, Dec 20, 2014 at 2:00 PM, Dennis Brakhane
>> > <brakhane at googlemail.com>
>> > wrote:
>> >>
>> >> Maybe I'm missing something, but wouldn't type hinting as it's defined
>> >> now break "virtual subclassing" of ABC?
>> >>
>> >> For example, given the following code:
>> >>
>> >>   from collections import Sequence
>> >>
>> >>   class MySequence:
>> >>     ...
>> >>
>> >>   Sequence.register(MySequence)
>> >>
>> >> it seems to me like the following would work:
>> >>
>> >>   def foo(bar):
>> >>       if not isinstance(bar, Sequence):
>> >>           raise RuntimeError("Foo can only work with sequences")
>> >>       ...
>> >>
>> >> but when rewritten for static type checking
>> >>
>> >>     def foo(bar: Sequence):
>> >>         ....
>> >>
>> >> it would cease to work. At least I don't see a way a static type
>> >> checker
>> >> could handle this relaiably (the register call might occur anywhere,
>> >> after all)
>> >>
>> >> Is this intentional?
>> >>
>> >> Even if this might be more a mypy/implementation question, it should be
>> >> clear to users of typing.py if they should expect ABCs to break or not
>> >
>> >
>> > Well, the program will still run fine with CPython, assuming you keep
>> > the
>> > isinstance() check in your program. The argument declaration does not
>> > cause
>> > calls with non-Sequence arguments to be rejected, it just guides the
>> > static
>> > checker (which is a program that you must run separately, in a similar
>> > way
>> > as a linter -- it is not built into CPython).
>> >
>> > The static checker may request the call foo(MySequence()) if it cannot
>> > see
>> > that MySequence is a Sequence. You have two options there: if you can
>> > change
>> > the code of MySequence, you should just inherit from Sequence rather
>> > than
>> > using the register() call; if you cannot change the code of MySequence,
>> > you
>> > should use a *stub* module which declares that MySequence is a Sequence.
>> > You
>> > can read up on stub modules in the mypy docs:
>> > http://mypy.readthedocs.org/en/latest/basics.html#library-stubs
>> >
>> > --
>> > --Guido van Rossum (python.org/~guido)
>> >
>> > _______________________________________________
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>>
>>
>>
>> --
>> Thanks,
>> Andrew Svetlov
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-- 
Thanks,
Andrew Svetlov