---
author: ''
category: ''
date: 2013/03/08 18:13:41
description: It's a dictionary! It's a function! It's a Fundict!
link: ''
priority: ''
slug: python-trick-the-fundict-or-the-diction
tags: python
title: 'Python Trick: the Fundict (or the Diction)'
type: text
updated: 2013/03/08 18:13:41
url_type: ''
---
Suppose you have made the choice in the past of exposing a dictionary as
part of an object's interface. So, people are doing things like::

    object.data[foo]['bar']

And now you want people to not have to specify ``foo`` because it can be obtained
from somewhere else. In fact, what you want now is to expose something like this::

    object.data(bar, foo='foo')

Here's an idea on how to do that *without breaking the old code*:

.. code:: python

    class fundict(dict):
        def __call__(self, bar, foo='foo'):
            return self[foo][bar]

That's a dictionary that's also a callable, and thus indistinguishable from a function.
A function-dictionary. A fundict.  And of couse, you could also do it the other way
around, and implement a function that works as a dictionary. A dictionary-function,
a diction. But since that's more work, I used this one.