[PEAK] Debugging code that uses PyProtocols

[Phillip J. Eby]

At 09:28 PM 2/19/04 -0500, Bob Ippolito wrote:
>I was wondering.. it can often be time consuming to track down a problem 
>if you forget to implement a protocol, are missing an adapter, etc.  Are 
>there any introspection facilities for PyProtocols for debugging 
>purposes... such as "what protocols does this object directly support", 
>"what is the adapter path from protocol A to protocol B", etc.
>
>It would be great to add this kind of facility to an IDE or something.. 
>make graphviz output, etc.

I deliberately avoided providing this type of introspection because it's an 
attractive nuisance.  A lot of what I consider mis-design in Zope is based 
on introspecting things that are not anybody's business but the object 
involved.  So, one of my goals for PyProtocols was to emphatically 
demonstrate that interface introspection is almost never necessary, and 
that designs that don't rely on it are more flexible and robust.

I did, however, leave hooks for persons with an appropriate level of 
motivation to add introspection capabilities to their *own* objects.  For 
example, if you implement protocols.IOpenProvider (instances) or 
protocols.IOpenImplementor (classes), you can receive information about 
declarations that are made.  You can also implement 
protocols.IImplicationListener and register to receive implication 
declarations that occur between interfaces.

You can also create a subclass of InterfaceClass, and use it as the 
metaclass for your interfaces, adding introspection methods.  Or better 
yet, just define an introspection interface, and declare an adapter to 
adapt InterfaceClass to your introspection interface.

So, if you want those types of facilities, they're really not that far 
away.  I just haven't run into any use cases for them personally as 
yet.  Even if I do, the odds are very good that I will not make them part 
of the PyProtocols API, though.  I'll probably bury them in some obscure 
location to avoid tempting people.  :)