[Zope-dev] adapting to None

[Chris Withers]

Marius Gedminas wrote:
> doesn't fail with an exception, I can assume that
> 
>   ISomeInterface.providedBy(adapter)

...which in this case should return True, as None does indeed implement 
the interface in question.

>> *That's* what I'm looking for help with, not judgement on whether 
>> adapting to None is a good idea or not ;-)
> 
> Could you please describe the real problem you're solving?  

I have a generic IFieldType (well, could arguably be called IFieldValue) 
adapter, which subclasses, eg:

class IFieldType(Interface): pass

class number(IFieldType): pass

class text(IFieldType): pass

class date(IFieldType): pass

class empty(IFieldType): pass

...etc..

The idea being that you can do things like:

text(anything)

...and if there's an adapter for it, it gets called and you get back 
something that implements IFieldType.

This couples nicely with, for example:

classImplements(unicode,text_type)
classImplements(int,number_type)
classImplements(float,number_type)
classImplements(date,date_type)
classImplements(type(None),empty)

def str_to_date(str):
     return parse(str,dayfirst=True)

provideAdapter(str_to_date,(str,),date)

Now, you could, for example, then do:

IFieldType([])

...which should return None.

cheers,

Chris

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