Container Objects Enforcing Contents

[Sean 'Shaleh' Perry]

On 13-Feb-2002 jim kraai wrote:
> Greetings,
> 
> I'm looking for suggestions on making container objects which must,
> may, or must not allow particular kinds of container objects to be
> added.
> 
> Any suggestions on a general approach for this?

Let's see .......

a constraints approach:

class Foo:
    def __init__(self, item):
        try:
            # look for a method of item that must exist
        except AttributeError:
            raise ConstraintException

This way you could add only items which support a method or have a certain
attribute.

You could also try to enforce types by ensuring the type of item matches types
you know about.  This often leads to a maintenance nightmare though.