[Python-Dev] static typing of input arguments in signatures

[Ethan Furman]

On 04/13/2014 04:58 PM, R. David Murray wrote:
> On Sun, 13 Apr 2014 15:59:36 -0400, Terry Reedy wrote:
>> On 4/13/2014 4:11 AM, Łukasz Langa wrote:
>>> On Apr 13, 2014, at 12:48 AM, Stefan Behnel wrote:
>>>>
>>>> So, what I've learned from seven years of Cython is that static typing in
>>>> signatures is actually less interesting than you might think at first
>>>> sight. It might be ok for documentation purposes, although its verboseness
>>>> makes that also a bit questionable.
>>>
>>> You raise a valid point that type hinting a dict instead of a Mapping is
>>> likely to create an overly limiting API. This sort of error is however
>>> quite easy to fix forward.
>>>
>>> To counter, we’ve had multiple data points during the summit suggesting
>>> that duck typing is not really that often used in production code. In
>>> other words, after initial prototyping and testing, an API of a callable
>>> gets settled and is later used with a very limited number of types.
>>
>> For public library code, where the use case is not known, apis should
>> usually be as generic as sensible. For private library code, I can
>> imagine that apis are and possibly even should be limited to classes
>> actually used. There naturally is a bit of a bias here for public code.
>
> The way *I* heard it was that types of the input arguments did not, in
> general, change *during the running of an application*.  That doesn't
> mean that the types wouldn't be different in a different application,
> which means that in a library that duck types, duck typing is indeed used
> in production, it's just that the types don't *change* for a production
> application.  So, yeah, pretty much what Terry said about library code
> versus application code.  That is, after all, what duck typing is about,
> and there is a *reason* we use it.

Personal experience:  I have my own copy of paramiko because it type checks for strings, and I routinely use a str-subclass.

--
~Ethan~