[Python-Dev] Not Deprecating Arbitrary Function Annotations

Mon Oct 5 17:17:33 EDT 2015

On Mon, 5 Oct 2015 at 13:55 Steve Wedig <stevewedig at gmail.com> wrote:

> Brett and Alexander,
>
> I am concerned about deprecation of arbitrary function annotations because
> Pep 484 suggests that two paths are under consideration. Here is the
> relevant section:
>
> "
> We do hope that type hints will eventually become the sole use for
> annotations, but this will require additional discussion and a deprecation
> period after the initial roll-out of the typing module with Python 3.5. The
> current PEP will have provisional status (see PEP 411 ) until Python 3.6 is
> released. The fastest conceivable scheme would introduce silent deprecation
> of non-type-hint annotations in 3.6, full deprecation in 3.7, and declare
> type hints as the only allowed use of annotations in Python 3.8. This
> should give authors of packages that use annotations plenty of time to
> devise another approach, even if type hints become an overnight success.
>
> Another possible outcome would be that type hints will eventually become
> the default meaning for annotations, but that there will always remain an
> option to disable them. For this purpose the current proposal defines a
> decorator @no_type_check which disables the default interpretation of
> annotations as type hints in a given class or function. It also defines a
> meta-decorator @no_type_check_decorator which can be used to decorate a
> decorator (!), causing annotations in any function or class decorated with
> the latter to be ignored by the type checker.
> "
>
> I am advocating against paragraph 1 (a deprecation path) and for the
> course of action stated in paragraph 2 :)
>

Fair enough, but since Python 3.5 is so new we have yet to gather any
feedback on the entire concept of type hints, let alone whether their use
is so broad and liked that we will consider dropping the decorators in
`typing` which mark alternative uses and define "function annotations" as
"type annotations" for everything.

So consider your view noted, but realize that the discussion of the uptake
of type hints has not started yet as it's premature to do so. If you want
to make sure to participate if/when the discussion of dropping support for
alternative uses of function annocations then consider staying subscribed
to python-dev to notice when that happens (but I suspect it will be a
while).

-Brett

>
>
>
>
> On Mon, Oct 5, 2015 at 1:23 PM, Guido van Rossum <guido at python.org> wrote:
>
>> Maybe I should clarify how the process of changing the language works.
>>
>> The PSF doesn't enter into it -- they manage the infrastructure (e.g.
>> mailing lists, Hg repo, tracker, python.org) but they don't have
>> anything to do with deciding how or when the language changes.
>>
>> Language changes are done *here* by *us* all. Anyone can write a PEP and
>> it will be discussed here (but first in python-ideas of course).
>>
>> I'm sorry you don't feel more included, but I really don't like the idea
>> of "us vs. them" in this list. We're all working together to make Python
>> the best language it can be.
>>
>> --Guido
>>
>> On Mon, Oct 5, 2015 at 1:18 PM, Ryan Gonzalez <rymg19 at gmail.com> wrote:
>>
>>> PSF. Nothing personal, of course...
>>>
>>>
>>> On October 5, 2015 3:01:11 PM CDT, Guido van Rossum <guido at python.org>
>>> wrote:
>>>>
>>>> "They"?
>>>>
>>>> On Mon, Oct 5, 2015 at 12:57 PM, Ryan Gonzalez <rymg19 at gmail.com>
>>>> wrote:
>>>>
>>>>> There is one reason I would be really freaking mad if they deprecated
>>>>> other uses of annotations:
>>>>>
>>>>> https://pypi.python.org/pypi/plac
>>>>>
>>>>> On October 5, 2015 1:55:37 PM CDT, Steve Wedig <stevewedig at gmail.com>
>>>>> wrote:
>>>>> >Congratulations on the release of 3.5 and Pep 484. I've used Python
>>>>> >professionally for 10 years and I believe type hints will make it
>>>>> >easier to
>>>>> >work with large codebases evolving over time. My only concern about
>>>>> Pep
>>>>> >484
>>>>> >is the discussion of whether or not to deprecate arbitrary function
>>>>> >annotations.
>>>>> >https://www.python.org/dev/peps/pep-0484/
>>>>> >
>>>>> >I would like to request that arbitrary function annotations are not
>>>>> >deprecated for three reasons:
>>>>> >1. Backwards Compatibility
>>>>> >2. Type Experimentation
>>>>> >3. Embedded Languages
>>>>> >
>>>>> >1. Backwards Compatibility
>>>>> >After reading Pep 3107 my team has made significant use of
>>>>> non-standard
>>>>> >annotations. It would be a serious burden to be forced to port our
>>>>> >annotations back to decorators. This would also make our codebase
>>>>> >considerably less readable because function annotations are much more
>>>>> >readable than input/output annotations relegated to decorators.
>>>>> >https://www.python.org/dev/peps/pep-3107/
>>>>> >
>>>>> >2. Type Experimentation
>>>>> >Arbitrary function annotations allow developers to experiment with
>>>>> >potential type system improvements in real projects. Ideas can be
>>>>> >validated
>>>>> >before officially adding them to the language. This seems like an
>>>>> >advantage
>>>>> >that should be preserved. After all, Pep 484 says it was strongly
>>>>> >inspired
>>>>> >by MyPy, an existing project.
>>>>> >http://mypy-lang.org/
>>>>> >
>>>>> >3. Embedded Languages
>>>>> >Python's flexibility makes it an amazing language to embed other
>>>>> >languages
>>>>> >in. In this regard, Python 3's addition of arbitrary function
>>>>> >annotations
>>>>> >and class decorators complements Python 2's dynamic typing, function
>>>>> >decorators, reflection, metaclasses, properties, magic methods,
>>>>> >generators,
>>>>> >and keyword arguments. Arbitrary function annotations are a crucial
>>>>> >part of
>>>>> >this toolkit, and this feature is not available in most other
>>>>> >languages.
>>>>> >For anyone interested in the utility and mechanics of embedded
>>>>> >languages,
>>>>> >I'd recommend Martin Fowler's book: Domain Specific Languages.
>>>>> >
>>>>> http://www.amazon.com/Domain-Specific-Languages-Addison-Wesley-Signature-Series/dp/0321712943
>>>>> >
>>>>> >So I agree with the course of action mentioned in Pep 484 that avoids
>>>>> >runtime deprecation of arbitrary function annotation: "Another
>>>>> possible
>>>>> >outcome would be that type hints will eventually become the default
>>>>> >meaning
>>>>> >for annotations, but that there will always remain an option to
>>>>> disable
>>>>> >them." I would only add that there should be a way to disable type
>>>>> >checking
>>>>> >for an entire directory (recursively). This would be useful for
>>>>> >codebases
>>>>> >that have not been ported to standard annotations yet, and for
>>>>> >codebases
>>>>> >that will not be ported for the reasons listed above.
>>>>> >
>>>>> >Thanks for your consideration.
>>>>> >
>>>>> >Best,
>>>>> >Steve
>>>>> >
>>>>> >
>>>>>
>>>>> >------------------------------------------------------------------------
>>>>> >
>>>>> >_______________________________________________
>>>>> >Python-Dev mailing list
>>>>> >Python-Dev at python.org
>>>>> >https://mail.python.org/mailman/listinfo/python-dev
>>>>> >Unsubscribe:
>>>>> >https://mail.python.org/mailman/options/python-dev/rymg19%40gmail.com
>>>>>
>>>>> --
>>>>> Sent from my Nexus 5 with K-9 Mail. Please excuse my brevity.
>>>>> _______________________________________________
>>>>> Python-Dev mailing list
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>>>>>
>>>>
>>>>
>>>>
>>> --
>>> Sent from my Nexus 5 with K-9 Mail. Please excuse my brevity.
>>>
>>
>>
>>
>> --
>> --Guido van Rossum (python.org/~guido)
>>
>
>
>
> --
> Steve Wedig
> stevewedig.com
> linkedin.com/in/wedig <http://www.linkedin.com/in/wedig>
>
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