[Tutor] Data Type with Dictionary and List Behavior

[John Fouhy]

On 28/03/06, Carroll, Barry <Barry.Carroll at psc.com> wrote:
>     1. Access by name         (dict)
>     2. Access by position     (list)
>     3. Addition of new items  (dict, list)
>     4. Set a 'last used' item (??????)
>     5. Set a 'default' item   (dict???)

Probably your best bet is to define your own container class.  If you
define __getitem__, you can use [] with instances of your class, just
like lists or dicts.

Something like this, perhaps (untested):

class MaskDict(UserDict.DictMixin):
    def __init__(self):
        self.keys = []
        self.data = {}
        self.default = None

    def __getitem__(self, key):
        if isinstance(key, (int, long)):
            self.default = self.keys[key]
            return self.data[self.default]
        else:
            self.default = key
            return self.data[key]

    def __setitem__(self, key, value):
        try:
            self.keys.remove(key)
        except ValueError:
            pass

        self.keys.append(key)
        self.data[key] = value

    def __delitem__(self, key, value):
        del self.data[key]
        self.keys.remove(key)

    def keys(self):
        return self.keys

    def setDefault(self, key):
        self.default = key

HTH!

--
John.