deferred_mappings.py 文件源码

def __init__(self, func, items, cache=True):
        """Applies the given function on the given items at the moment of data request.

        On the moment one of the keys of this dict class is requested we apply the given function on the given items
        and return the result of that function. The advantage of this class is that it defers an expensive operation
        until it is needed.

        Items added to this dictionary after creation are assumed to be final, that is, we won't run the
        function on them.

        Args:
            func (Function): the callback function to apply on the given items at request, with signature:

                .. code-block:: python

                    def callback(key, value)

            items (collections.MutableMapping): the items on which we operate
            cache (boolean): if we want to cache computed results
        """
        self._func = func
        self._items = copy.copy(items)
        self._applied_on_key = {}
        self._cache = cache