[Python-ideas] check interfaces, isducktype(X, A)

[Gregory Salvan]

@Serhiy
Not really (only with FooReader, BarReader) as it checks if functions
co_argcount and co_kwonlyargcount are equals.
In this case it requires BazReader.__ducktypecheck__ to be implemented.

I had a doubt when doing this, I agree with you isducktype(BazReader,
FooReader) can return True (whereas  isducktype(FooReader, BazReader)
should stay false)
This can easily be changed.

@Oleg:
The fact there is a lot of interface implementations means certainly it's
something needed.
Each implementation I've seen add burden on objects whereas the only thing
personnally I need, is to be sure I'll be able to call some methods off
injected objects.

@spir:
Names can easily be checked, but I can't see why doing this, it add
constraints to developpers without adding safety.

@Andrew +1
Maybe inspect is more appropriate as it provides ArgSpec and getmembers ?

My code is crappy, I've just do it like that to train me in C then tought
it might be interesting to get feedback.


2013/12/2 Serhiy Storchaka <storchaka at gmail.com>

> 02.12.13 17:55, Gregory Salvan написав(ла):
>
>  Hi,
>> I've made a try of a function that check object/class members for duck
>> typing.
>>
>> For now I've basically called it isducktype(X, A)
>> it returns true if:
>> - X has all attributes of A
>> - X methods have same number of arguments than corresponding A methods
>>
>> or if A.__ducktypecheck__(X) returns True
>>
>> Behaviour looks like isinstance and issubclass (support tuples...).
>>
>
> class FooReader:
>     def read(self, n=None): ...
>
> class BarReader:
>     def read(self, amount=-1): ...
>
> class BazReader:
>     def read(self, size=-1, chars=-1, firstline=False): ...
>
> Instances of all three classes can be used where needed an object with the
> read() method which are called with one positional argument or without
> arguments. Is it possible to use isducktype() for such case?
>
>
>
> _______________________________________________
> Python-ideas mailing list
> Python-ideas at python.org
> https://mail.python.org/mailman/listinfo/python-ideas
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-ideas/attachments/20131203/da9facc3/attachment-0001.html>