utils.py

try:
    frozenset
except NameError:
    #Import from the sets module for python 2.3
    from sets import Set as set
    from sets import ImmutableSet as frozenset

class MethodDispatcher(dict):
    """Dict with 2 special properties:

    On initiation, keys that are lists, sets or tuples are converted to
    multiple keys so accessing any one of the items in the original
    list-like object returns the matching value

    md = MethodDispatcher({("foo", "bar"):"baz"})
    md["foo"] == "baz"

    A default value which can be set through the default attribute.
    """

    def __init__(self, items=()):
        # Using _dictEntries instead of directly assigning to self is about
        # twice as fast. Please do careful performance testing before changing
        # anything here.
        _dictEntries = []
        for name,value in items:
            if type(name) in (list, tuple, frozenset, set):
                for item in name:
                    _dictEntries.append((item, value))
            else:
                _dictEntries.append((name, value))
        dict.__init__(self, _dictEntries)
        self.default = None

    def __getitem__(self, key):
        return dict.get(self, key, self.default)