[Zope-dev] Blobs and modes

[Jacob Holm]

Hi Benji and Roger

Roger Ineichen wrote:
> Hi Benji
>
> My comment is absolutly of topic. Just skip it
> if you don't have time...
>
>   
Staying on the off-topic...

> I agree on not describe the constructor signature. But I can't 
> agree on the reason why.
>
> If you have to use an existing framework with defined interfaces
> the missing constructor signature doesn't make sence if the
> framework at the same time offers implementations which use
> a specific signature. It's just a leak of information.
>
> I'm also against describing the __init__ signature in an 
> interfaces but there is another reason. 
>
> The missing __init__ signature in the interfaces make only 
> sense if it comes to reduce the variants of it. It whould 
> not be helpful to have several different named interfaces 
> just because they support another constructor signature.
>
> But describing a constructor signature is not in general a 
> bad thing.
>
>   
What I think you are saying is that you also want to have the signature 
for the object factory somewhere. That makes good sense, but usually 
isn't part of the API for the the object itself. It belongs in a 
different interface that is used by those that *create* the objects, 
rather than *use* the objects. So you can have any number of interfaces 
for creating the object, and a single interface for working on the 
object once it is there. That makes a lot of sense to me.

<rant>Unfortunately the __init__ method plays a dual role in python. It 
defines the constructor signature and is called automatically by the 
*real* constructor (which I would argue is the __call__ method on the 
type, at least for new-style objects). However, it is also a regular 
instance method that can be called from anywhere, and so is in a sense a 
part of the API for the object. I believe this dualism is the root of 
much evil, or at least confusion, whenever "super" calls and/or 
interfaces are being discussed.</rant>

That said, and returning to the original issue. I don't see the reason 
why Blob.open shouldn't just ignore the 'b' flag and just give an error 
if someone tries to give it a 't'. If that makes it useful in more 
cases, I'd be all for it.

Regards
Jacob Holm