Inheriting dictionary

Simon Forman sajmikins at gmail.com
Wed Aug 19 00:08:11 CEST 2009


On Aug 18, 3:44 pm, Pavel Panchekha <pavpanche... at gmail.com> wrote:
> I want a dictionary that will transparently "inherit" from a parent
> dictionary. So, for example:
>
> """
> a = InheritDict({1: "one", 2: "two", 4: "four"})
> b = InheritDict({3: "three", 4: "foobar"}, inherit_from=a)
>
> a[1] # "one"
> a[4] # "four"
> b[1] # "one"
> b[3] # "three"
> b[4] # "foobar"
> """
>
> I've written something like this in Python already, but I'm wondering
> if something like this already exists, preferably written in C, for
> speed.


I would consider something like the following:


a = {1: "one", 2: "two", 4: "four"}
b = {3: "three", 4: "foobar"}


from functools import partial


def getter(first, second, key):
    try:
        return first(key)
    except KeyError:
        return second(key)


f = partial(getter, b.__getitem__, a.__getitem__)


# Or, if you know you'll be getting a lot of KeyErrors, you
# can use get() instead of __getitem__().

def getter1(first, second, key, sentinel=None):
    item = first(key, sentinel)
    if item is sentinel:
        item = second(key)
    return item

g = partial(getter1, b.get, a.__getitem__)


HTH,
~Simon



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