Metaclasses vs. standard Python reflection?

[Carl Banks]

tweedgeezer at hotmail.com (Jeremy Fincher) wrote in message news:<698f09f8.0305012053.123ead56 at posting.google.com>...
> I've been looking for examples of metaclasses I can use for a talk I'm
> going to be giving next week, but I've been having trouble finding
> examples that solve problems that wouldn't just as easily be via
> Python's uber-reflective __getattr__/__setattr__ and inheritance. 
> Does anyone have a good example of a problem that's solved more
> "beautifully" with metaclasses than with Python's standard reflection
> facilities?


What if you want a class whose bases come out of a tuple?  Maybe you
want to determine its bases on the fly.  You can't do that with
getattr/setattr.  You can do it with the "new" module, but a much more
beautiful way is to use a metaclass:


    class BaseIsATuple(type):
        def __new__(self,name,bases,clsdict):
            assert len(bases) == 1
            return type.__new__(self,name,tuple(bases[0]),clsdict)


Then:

    dynabases = some_dynamic_calculation_yielding_a_tuple()

    class Something(dynabases):
        __metaclass__ = BaseIsATuple


-- 
CARL BANKS