Are there 'Interfaces' in Python??

[Markus Schaber]

Hi,

Richard Jones <richard at bizarsoftware.com.au> schrub:

> On Wednesday 26 September 2001 11:50, Paul Rubin wrote:
>> "tszeto" <tszeto at mindspring.com> writes:
>> > Was wondering if Python supported 'Interfaces' (something akin to
>> > Java interfaces)? Or if there's a workaround to get the same thing.
>>
>> Java interfaces are a workaround for java's non-support of multiple
>> base classes in objects.  Python supports multiple base classes, so
>> it doesn't need a workaround for their absence.
> 
> Er, no. They may be percieved as that, but since interfaces can't
> actually _do_ anything, whereas multiple inheritance _can_, I believe
> this is a dead herring.

It gets even somehow perverse in java: interfaces can bring code with 
them in the never java versions, using inner classes:

public interface container {
  public class embedded {
    public void test() {
      System.out.println("Hello");
    }
  }
}

> Interfaces are an extremely useful form of "type" checking for OO
> systems. Python already has "interfaces" in the form of agreed methods
> - witness the "pass a file-like object" requirements in a lot of APIs.
> An interface would just formalise that.

That is correct. In a lot of cases, such interfaces are a helpful 
instrument to find bugs, because they force such agreements. But the 
way they are implemented in Java, those are not as flexible as someone 
could wish it in some cases. Python doesn't enforce anything, thus the 
programmer has to know what he does - but he also can do whatever he 
wants because he knows what he does.

markus
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