keyeditems.py

class KeyedItems(dict):
    """
    KeyedItems allow you to create a dict from a list of dicts, keyed by the parameter passed
    as key. If no param is passed the entire item will be the key. KeyedItems will
    not process the entire list, but processing will only proceed up to the item
    that you requested was found, saving memory and processing time.

    This is demonstrated below by using an infinite list generated by count.

    >>> from itertools import count
    >>> x = KeyedItems(({"koe": y} for y in count()), key="koe")
    >>> x.get(4)
    {'koe': 4}
    >>> a = KeyedItems(count())
    >>> a.get(100)
    100
    """

    def __init__(self, items, key=None):
        # use an iterator so the list can only be traversed once.
        self.items = iter(items)
        self.key = key

    def get(self, key, default=None):
        try:
            return self[key]
        except KeyError:
            for item in self.items:
                item_key = item[self.key] if self.key else item
                self[item_key] = item
                if item_key == key:
                    return item

        return default